Add refusal

[qhenkart]

Describe the change
With structured outputs, the OpenAI API has added the "refusal" field where user generated prompt failures show up. This is clearly defined in the documentation: https://platform.openai.com/docs/guides/structured-outputs/refusals but not present in the SDK

Provide OpenAI documentation link
Provide a relevant API doc from https://platform.openai.com/docs/api-reference

Describe your solution
I simply added the missing field

Tests
n/a

Additional context
n/a

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.01%. Comparing base (774fc9d) to head (507d5cd).
Report is 48 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #844      +/-   ##
==========================================
+ Coverage   98.46%   99.01%   +0.55%     
==========================================
  Files          24       26       +2     
  Lines        1364     1422      +58     
==========================================
+ Hits         1343     1408      +65     
+ Misses         15        8       -7     
  Partials        6        6              

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[sashabaranov]

Thank you!