Updates the tool call struct

[albertpurnama]

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Describe the change

Querying run steps will create marshalling error like:
json: cannot unmarshal array into Go struct field StepDetails.data.step_details.tool_calls of type openai.StepDetailsToolCalls

The official docs of the run steps points to using arrays instead of wrapping tool_calls in an object.

Here's the actual response of fetching run step:

Describe your solution
This PR addresses this by removing the extra wrapping object around tool_calls property.

Tests
N/A

Additional context

Issue: No issues created yet, should I create one? 🤔

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1846572) 98.38% compared to head (02d014e) 98.38%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #595   +/-   ##
=======================================
  Coverage   98.38%   98.38%           
=======================================
  Files          24       24           
  Lines        1300     1300           
=======================================
  Hits         1279     1279           
  Misses         15       15           
  Partials        6        6           

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[sashabaranov]

Thank you for the PR!