feat: support tool calls

[northes]

Describe the change

Support for tool calls and a simple example.

Provide Moonshot documentation link

https://platform.moonshot.cn/docs/api/tool-use

Additional context

Close: #16

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 75.22%. Comparing base (85f703d) to head (a5ab186).
Report is 4 commits behind head on main.

Files	Patch %	Lines
chat_completions_builder.go	84.61%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #19      +/-   ##
==========================================
+ Coverage   71.08%   75.22%   +4.13%     
==========================================
  Files          11       11              
  Lines         377      440      +63     
==========================================
+ Hits          268      331      +63     
  Misses         60       60              
  Partials       49       49              

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