ai: update llm tokens used

[rickstaa]

What does this pull request do? Explain your changes. (required)

Important

Merge #3336 and livepeer/ai-worker#402 first and release runner v0.13.2.

This pull request updates the codebase to use the new LLM OpenAPI spec, which replaces tokens_used with usage. See livepeer/ai-worker#402 for more details.

Specific updates (required)

• Updates ai_process.go to use the new ai-worker client bindings.
• Updates LLM tests

How did you test each of these updates (required)

Run an on-chain Gateway and Orchestrator.

Does this pull request close any open issues?

No, but it implements the change discussed in https://discordapp.com/channels/423160867534929930/1319248702032056383/1332619710562439168.

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[ad-astra-video]

Tested with updated go.sum after merger livepeer/ai-worker PR #402 locally streaming and non-streaming responses.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 33.69623%. Comparing base (1065885) to head (d849d51).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
server/ai_process.go	0.00000%	3 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3372         +/-   ##
===================================================
+ Coverage   33.69179%   33.69623%   +0.00444%     
===================================================
  Files            141         141                 
  Lines          37475       37476          +1     
===================================================
+ Hits           12626       12628          +2     
+ Misses         24127       24126          -1     
  Partials         722         722                 

Files with missing lines	Coverage Δ
server/ai_process.go	0.59880% <0.00000%> (-0.00052%)	⬇️

... and 2 files with indirect coverage changes

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Files with missing lines	Coverage Δ
server/ai_process.go	0.59880% <0.00000%> (-0.00052%)	⬇️

... and 2 files with indirect coverage changes