Allow structured outputs via function calling

[greysteil]

Describe the change

Allows strict: true to be passed to OpenAI within a function's definition, triggering OpenAI's new structured outputs setup to ensure the function's schema is strictly adhered to.

Provide OpenAI documentation link

https://openai.com/index/introducing-structured-outputs-in-the-api/

Describe your solution

Add Strict to the properties of FunctionDefinition. Only serialise it in the JSON if its value is true (to avoid wasting tokens).

Tests
Added a test.

Additional context
None

[greysteil]

@sashabaranov the linting error on my first commit wasn't related to this PR. I've fixed it in the second commit since it was a trivial one.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.00%. Comparing base (774fc9d) to head (76e5279).
Report is 41 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #828      +/-   ##
==========================================
+ Coverage   98.46%   99.00%   +0.54%     
==========================================
  Files          24       26       +2     
  Lines        1364     1410      +46     
==========================================
+ Hits         1343     1396      +53     
+ Misses         15        8       -7     
  Partials        6        6              

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[sashabaranov]

@greysteil thank you for the PR! Could you please fix the merge conflict and add an integration test — it's pretty hard to follow all the OpenAI API updates these days

[greysteil]

@sashabaranov done!