Feature/chromadb embedding functions #6267

[tejas-dharani]

Why are these changes needed?

This PR adds support for configurable embedding functions in ChromaDBVectorMemory, addressing the need for users to customize how embeddings are generated for vector similarity search. Currently, ChromaDB memory is limited to default embedding functions, which restricts flexibility for different use cases that may require specific embedding models or custom embedding logic.

The implementation allows users to:

• Use different SentenceTransformer models for domain-specific embeddings
• Integrate with OpenAI's embedding API for consistent embedding generation
• Define custom embedding functions for specialized requirements
• Maintain backward compatibility with existing default behavior

Related issue number

Closes #6267

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov]

Codecov Report

Attention: Patch coverage is 86.36364% with 9 lines in your changes missing coverage. Please review.

Project coverage is 79.67%. Comparing base (150ea01) to head (49de936).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...n-ext/src/autogen_ext/memory/chromadb/_chromadb.py	66.66%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6648      +/-   ##
==========================================
+ Coverage   79.65%   79.67%   +0.01%     
==========================================
  Files         229      231       +2     
  Lines       17126    17172      +46     
==========================================
+ Hits        13642    13682      +40     
- Misses       3484     3490       +6     

Flag	Coverage Δ
unittests	79.67% <86.36%> (+0.01%)	⬆️

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[victordibia]

@tejas-dharani ,

Thanks again for the PR.
I made some changes, feel free to test them and then we can merge it in

• Removed changes to files unrelated to the PR
• Refactored to a folder structure (provides a better structure to extend in the future)
• Updated the Memory notebook to include an example (instead of a standalone example file)
• Updated the tests.

[tejas-dharani]

@victordibia ,

Thanks for the updates!

• Fixed the syntax error validation in tests (made it platform-agnostic)
• The refactoring to folder structure looks great
• Memory notebook integration is a nice improvement

[victordibia]

Thanks for the work on this @tejas-dharani , much appreciated.
For future PR's it would be great if we ONLY added commits related to the focus/topic of the PR.
For example, the commit to the dotnet package or the change to the code executor tests are unrelated to this PR and should not be part of it. In these cases, we should ideally create separate PRs.

Thanks again!

[tejas-dharani]

@victordibia Thanks for the feedback and for taking the time to review the PR!

You're absolutely right about keeping commits focused - I'll make sure to separate unrelated changes into their own PRs going forward.