Update Mistral client class to support new Mistral v1.0.1 package

[marklysze]

Mistral AI released an updated python client package, v1.0.1, which had breaking changes to code using versions before then. This updated Mistral client class has been updated to support the new version.

No new functionality has been added, but prices have been updated.

Why are these changes needed?

Existing code will not work with the latest Mistral AI (mistralai) package.

Related issue number

None, yet :).

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.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[Hk669]

lgtm. thanks @marklysze for the updates.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 6.66667% with 28 lines in your changes missing coverage. Please review.

Project coverage is 44.88%. Comparing base (3fc708d) to head (ca334a9).

Files	Patch %	Lines
autogen/oai/mistral.py	6.66%	28 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #3356       +/-   ##
===========================================
+ Coverage   33.33%   44.88%   +11.55%     
===========================================
  Files          95       95               
  Lines       10661    10669        +8     
  Branches     2278     2453      +175     
===========================================
+ Hits         3554     4789     +1235     
+ Misses       6791     5408     -1383     
- Partials      316      472      +156     

Flag	Coverage Δ
unittest	12.10% <6.66%> (?)
unittests	44.19% <6.66%> (+10.87%)	⬆️

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[randombet]

LGTM.