Allow usage of ObjectSerializer for Cosmos bindings

[jviau]

Issue describing the changes in this PR

resolves #2911

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Additional information

Addresses an issue with CosmosDB extension where users could not customize JSON serialization when binding directly to a POCO.

Issue:

CosmosDBConverter was not consuming any user-provided JSON serialization customization. This was a regression from #1924.

Fix:

1. Add a new option to CosmosDBExtensionOptions to provide a ObjectSerializer, defaulting to WorkerOptions.Serializer if no serializer is explicitly set.
2. Update CosmosDBConverter to use this new serializer when deserializing POCOs

Concerns / Discussion:

This is a fix for a regression introduced back in December 2023. But it COULD be seen as a new breaking behavior change for some customers. This poses some risk for this change.

[jviau]

Re-opening. I have reverted back to opt-in for this change.

[Copilot]

Pull request overview

This PR addresses a regression in the CosmosDB extension where custom JSON serialization settings from WorkerOptions.Serializer were not being used when deserializing POCOs in CosmosDB bindings. The fix introduces a new Serializer property to CosmosDBExtensionOptions and a helper method UseCosmosDBWorkerSerializer() to explicitly opt-in to using the worker's serializer for CosmosDB POCO deserialization.

Key changes:

• Added ObjectSerializer? Serializer property to CosmosDBExtensionOptions for custom serialization
• Introduced UseCosmosDBWorkerSerializer() extension method to configure the serializer
• Refactored CosmosDBConverter to use the configured serializer instead of hardcoded System.Text.Json
• Fixed a bug in WorkerCosmosSerializer.FromStream() where streams were being disposed prematurely
• Maintained backward compatibility via a DefaultSerializer with PropertyNameCaseInsensitive = true

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
WorkerCosmosSerializer.cs	Fixed stream disposal bug for Stream-type bindings and minor style improvements
FunctionsWorkerApplicationBuilderExtensions.cs	Added UseCosmosDBWorkerSerializer() method and updated serializer configuration logic
CosmosDBConverter.cs	Replaced hardcoded System.Text.Json with configurable ObjectSerializer throughout
CosmosDBExtensionOptions.cs	Added public Serializer property with TODO for future default behavior
CosmosDBBindingOptions.cs	Added DefaultSerializer and Serializer property getter for fallback behavior
CosmosDBBindingOptionsSetup.cs	Removed unused import and formatting cleanup
release_notes.md	Updated version placeholder and release note description

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[brettsam]

No objections to the changes, but would love to see tests added around this, especially since it looks like we broke behavior at one point.

[jviau]

@brettsam unit tests have been added. I verify the new options setup in one test class, and then added converter tests to verify the resolved serializer is used for the POCO case.