Cosmos: Fix replaceItem bypassing customItemSerializer

[lloydmeta]

Description

CosmosAsyncContainer.replaceItem eagerly converted the POJO to a Document via
InternalObjectNode.fromObject(item), which serialises through the SDK's internal
ObjectMapper rather than the user's customItemSerializer. The resulting Document
then short-circuits Document.fromObject (already a Document, returned as-is),
so the custom serialiser is never invoked.

This means any ObjectMapper configuration on the custom serialiser (e.g.
WRITE_DATES_AS_TIMESTAMPS = false, JsonInclude.NON_NULL, custom modules) is
silently ignored for replaceItem, while createItem and upsertItem work correctly.

The fix removes the intermediate InternalObjectNode.fromObject conversion and passes
the raw POJO through the replace chain, matching how createItem and upsertItem
already work.

Fixes #48527

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[github-actions]

Thank you for your contribution @lloydmeta! We will review the pull request and get back to you soon.

[FabianMeiswinkel]

Looks goo to me - Thanks!

[kushagraThapar]

Thanks @lloydmeta for fixing this bug on the SDK, appreciate your contributions.

[kushagraThapar]

@lloydmeta the newly added tests are failing on this pipeline, can you please check and fix them? https://dev.azure.com/azure-sdk/public/_build/results?buildId=6048391&view=ms.vss-test-web.build-test-results-tab&runId=60434280&paneView=debug
Let me know if you can't access them, I can help pasting the specific error logs.

[Copilot]

Pull request overview

Fixes CosmosAsyncContainer.replaceItem to respect the effective (custom) item serializer by removing the eager POJO→Document conversion that bypassed user-provided customItemSerializer.

Changes:

• Updated replaceItem flow to pass the raw item object through the replace pipeline so Document.fromObject(..., effectiveItemSerializer) can invoke the correct serializer.
• Added an emulator test to validate replaceItem respects custom ObjectMapper settings (e.g., JsonInclude.NON_NULL).
• Added a CHANGELOG entry describing the bug fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/CosmosAsyncContainer.java	Stops pre-serializing items via SDK-internal mapper so replace operations use the effective/custom serializer.
sdk/cosmos/azure-cosmos/CHANGELOG.md	Documents the serializer-bypass bug fix under “Bugs Fixed”.
sdk/cosmos/azure-cosmos-tests/src/test/java/com/azure/cosmos/CosmosItemSerializerTest.java	Adds coverage ensuring replaceItem honors request-level custom serializer/ObjectMapper behavior.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.