Add ChatCompletionCache along with AbstractStore for caching completions

[srjoglekar246]

Why are these changes needed?

Add a caching wrapper to ChatCompletionClient, that can use any store with get/set methods for storage.

Related issue number

Closes #4752

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• Added unit tests

Copilot reviewed 5 out of 6 changed files in this pull request and generated no comments.

Files not reviewed (1)

• python/packages/autogen-core/src/autogen_core/store/abstract_store_base.py: Evaluated as low risk

[srjoglekar246]

@ekzhu do we need any documentation changes? I suppose API Reference gets updated automatically?

[codecov]

Codecov Report

Attention: Patch coverage is 96.38554% with 3 lines in your changes missing coverage. Please review.

Project coverage is 68.68%. Comparing base (0446ce9) to head (97e8d66).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
...ages/autogen-core/src/autogen_core/_cache_store.py	71.42%	2 Missing ⚠️
...ges/autogen-core/src/autogen_core/models/_cache.py	98.41%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4924      +/-   ##
==========================================
+ Coverage   68.49%   68.68%   +0.19%     
==========================================
  Files         156      157       +1     
  Lines       10061    10137      +76     
==========================================
+ Hits         6891     6963      +72     
- Misses       3170     3174       +4     

Flag	Coverage Δ
unittests	68.68% <96.38%> (+0.19%)	⬆️

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[ekzhu]

Aside from API documentation. We can discuss the cache in the following places:

https://github.com/microsoft/autogen/blob/main/python/packages/autogen-core/docs/src/user-guide/agentchat-user-guide/tutorial/models.ipynb

https://github.com/microsoft/autogen/blob/main/python/packages/autogen-core/docs/src/user-guide/core-user-guide/framework/model-clients.ipynb

[srjoglekar246]

@ekzhu added docs as you mentioned :-)

[jackgerrits]

I think we should spend some more time to see if the interface can be improved. Especially if this is going into core

[ekzhu]

This section should come after the streaming and Azure Open AI subsections.

I think for the example we can show how to use diskcache as that's what most people will be using.

To add diskcache for building the doc we will need to include it in the doc dependencies in the core's pyproject.toml file.

[ekzhu]

Use:

.. code-bloc:: python

For the Python code. We will need to add redis and diskcache to the doc dependencies to build the doc, as we type check all the code blocks included in the API docs.