fix: unnecessary prevention of tool calls for finish reason

[willbakst]

Closes #256

• Noticed that we were unnecessarily preventing correct behavior if finish_reason not in ["tool_calls", "function_call"] even if tools were present.
• This prevented proper use of tool_choice="required" since it results (sometimes? always?) in finish_reason == "stop"
• Now instead we simply check if finish_reason == "length" so let the user know it failed to call the tool (if it was trying to) because it ran out of tokens.
• Made other similar changes for other providers

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (b74ed17) to head (a3bb545).

Additional details and impacted files

@@            Coverage Diff            @@
##               dev      #257   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          126       126           
  Lines         6371      6384   +13     
=========================================
+ Hits          6371      6384   +13     

Flag	Coverage Δ
tests	100.00% <100.00%> (ø)

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