fix: mask apiKey in OvhAiEmbeddingModel builder toString (#5608)

## Issue
Closes #5607

## Change
`OvhAiEmbeddingModel.OvhAiEmbeddingModelBuilder.toString()` printed the
API key in plain text via `", apiKey=" + this.apiKey`, so any log or
exception that renders the builder leaked the OVHcloud key. It now masks
the key, matching the merged sibling builders JinaEmbeddingModel
(#3680), JinaScoringModel/JinaClient (#5539), and NomicEmbeddingModel
(#5559):
- `", apiKey=" + (this.apiKey == null ? null : "********")`

A null key still renders as `apiKey=null` (no NPE); no other field is a
secret.

Added unit test `OvhAiEmbeddingModelTest` (JUnit 5 + AssertJ, no new
dependencies), mirroring `JinaScoringModelBuilderTest` from #5539:
- with a key set, `toString()` contains `apiKey=********` and not the
raw value
- with no key, `toString()` contains `apiKey=null`

Note: unlike Jina (constructors only), the whole `OvhAiEmbeddingModel`
class is `@Deprecated(forRemoval = true, since = "1.14.0")`. Masking is
still worthwhile to stop leaking the key while the class is in use. The
functional change is one line in `toString()`; the remaining file diff
is Spotless reformatting a previously unformatted file (`ratchetFrom
origin/main`), not manual edits. Module unit tests and `spotless:check`
pass; the `*IT` needs an API key and was not run.

## General checklist
- [X] There are no breaking changes (API, behaviour)
- [X] I have added unit and/or integration tests for my change
- [X] The tests cover both positive and negative cases
- [X] I have manually run all the unit and integration tests in the
module I have added/changed, and they are all green
- [ ] I have manually run all the unit and integration tests in the core
and main modules, and they are all green
- [ ] I have added/updated the documentation
- [ ] I have added an example in the examples repo (only for "big"
features)
- [ ] I have added/updated Spring Boot starter(s) (if applicable)

<!-- "Checklist for adding new maven module" and both embedding-store
checklists omitted: not applicable (this is a one-line fix to an
existing module, no new module and no embedding-store integration
change). -->

langchain4j-ovh-ai/src/main/java/dev/langchain4j/model/ovhai/OvhAiEmbeddingModel.java

@@ -1,5 +1,9 @@
 package dev.langchain4j.model.ovhai;
 
+import static dev.langchain4j.internal.RetryUtils.withRetryMappingExceptions;
+import static dev.langchain4j.internal.Utils.getOrDefault;
+import static java.util.stream.Collectors.toList;
+
 import dev.langchain4j.data.embedding.Embedding;
 import dev.langchain4j.data.segment.TextSegment;
 import dev.langchain4j.model.embedding.EmbeddingModel;
@@ -7,14 +11,9 @@ import dev.langchain4j.model.output.Response;
 import dev.langchain4j.model.ovhai.internal.api.EmbeddingRequest;
 import dev.langchain4j.model.ovhai.internal.api.EmbeddingResponse;
 import dev.langchain4j.model.ovhai.internal.client.DefaultOvhAiClient;
-import org.slf4j.Logger;
-
 import java.time.Duration;
 import java.util.List;
-
-import static dev.langchain4j.internal.RetryUtils.withRetryMappingExceptions;
-import static dev.langchain4j.internal.Utils.getOrDefault;
-import static java.util.stream.Collectors.toList;
+import org.slf4j.Logger;
 
 /**
  * @deprecated use {@code OpenAiEmbeddingModel} from {@code langchain4j-open-ai} module instead
@@ -26,16 +25,14 @@ public class OvhAiEmbeddingModel implements EmbeddingModel {
     private final int maxRetries;
 
     private OvhAiEmbeddingModel(OvhAiEmbeddingModelBuilder builder) {
-        this.client =
-                DefaultOvhAiClient
-                        .builder()
-                        .baseUrl(builder.baseUrl)
-                        .apiKey(builder.apiKey)
-                        .timeout(getOrDefault(builder.timeout, Duration.ofSeconds(60)))
-                        .logRequests(getOrDefault(builder.logRequests, false))
-                        .logResponses(getOrDefault(builder.logResponses, false))
-                        .logger(builder.logger)
-                        .build();
+        this.client = DefaultOvhAiClient.builder()
+                .baseUrl(builder.baseUrl)
+                .apiKey(builder.apiKey)
+                .timeout(getOrDefault(builder.timeout, Duration.ofSeconds(60)))
+                .logRequests(getOrDefault(builder.logRequests, false))
+                .logResponses(getOrDefault(builder.logResponses, false))
+                .logger(builder.logger)
+                .build();
         this.maxRetries = getOrDefault(builder.maxRetries, 2);
     }
 
@@ -56,17 +53,14 @@ public class OvhAiEmbeddingModel implements EmbeddingModel {
     @Override
     public Response<List<Embedding>> embedAll(List<TextSegment> textSegments) {
 
-        EmbeddingRequest request = EmbeddingRequest
-                .builder()
+        EmbeddingRequest request = EmbeddingRequest.builder()
                 .input(textSegments.stream().map(TextSegment::text).collect(toList()))
                 .build();
 
         EmbeddingResponse response = withRetryMappingExceptions(() -> client.embed((request)), maxRetries);
 
-        List<Embedding> embeddings = response.getEmbeddings()
-                .stream()
-                .map(Embedding::from)
-                .collect(toList());
+        List<Embedding> embeddings =
+                response.getEmbeddings().stream().map(Embedding::from).collect(toList());
 
         return Response.from(embeddings);
     }
@@ -80,8 +74,7 @@ public class OvhAiEmbeddingModel implements EmbeddingModel {
         private Boolean logResponses;
         private Logger logger;
 
-        OvhAiEmbeddingModelBuilder() {
-        }
+        OvhAiEmbeddingModelBuilder() {}
 
         public OvhAiEmbeddingModelBuilder baseUrl(String baseUrl) {
             this.baseUrl = baseUrl;
@@ -127,7 +120,10 @@ public class OvhAiEmbeddingModel implements EmbeddingModel {
         }
 
         public String toString() {
-            return "OvhAiEmbeddingModel.OvhAiEmbeddingModelBuilder(baseUrl=" + this.baseUrl + ", apiKey=" + this.apiKey + ", timeout=" + this.timeout + ", maxRetries=" + this.maxRetries + ", logRequests=" + this.logRequests + ", logResponses=" + this.logResponses + ")";
+            return "OvhAiEmbeddingModel.OvhAiEmbeddingModelBuilder(baseUrl=" + this.baseUrl + ", apiKey="
+                    + (this.apiKey == null ? null : "********") + ", timeout=" + this.timeout + ", maxRetries="
+                    + this.maxRetries + ", logRequests=" + this.logRequests + ", logResponses=" + this.logResponses
+                    + ")";
         }
     }
 }

langchain4j-ovh-ai/src/test/java/dev/langchain4j/model/ovhai/OvhAiEmbeddingModelTest.java

@@ -0,0 +1,22 @@
+package dev.langchain4j.model.ovhai;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class OvhAiEmbeddingModelTest {
+
+    @Test
+    void toString_should_mask_api_key() {
+        String toString = OvhAiEmbeddingModel.builder().apiKey("secret-api-key").toString();
+
+        assertThat(toString).doesNotContain("secret-api-key").contains("apiKey=********");
+    }
+
+    @Test
+    void toString_should_render_null_api_key_as_null() {
+        String toString = new OvhAiEmbeddingModel.OvhAiEmbeddingModelBuilder().toString();
+
+        assertThat(toString).contains("apiKey=null");
+    }
+}