## Summary
- Introduce a fluent `Builder` for `DoclingDocumentParser` with an
optional `Function<InBodyConvertDocumentResponse, String>`
(`documentTextExtractor`) to customize how document text is extracted
from the Docling conversion response
- Default behavior (markdown extraction) is preserved — the extractor
defaults to `response.getDocument().getMarkdownContent()`
- Deprecate the existing public constructors in favor of the builder,
delegating internally to the builder-based constructor
- Bump `docling-serve-api`/`docling-serve-client` version from 0.5.2 to
0.6.0
- Update documentation at
`docs/docs/integrations/document-parsers/docling.md` with builder usage
and custom extraction examples
## Test plan
- [x] All 17 unit tests pass (7 existing + 10 new) covering builder
construction, custom extractors (HTML, text, doctags), null/blank
extractor results, full response metadata access, and builder with
options
- [x] Integration test with custom extractor against real Docling
container (`DoclingDocumentParserIT`)
- [x] Verify backward compatibility — existing constructor-based tests
pass without modification
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Signed-off-by: Eric Deandrea <eric.deandrea@ibm.com>
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