[release/4.0] Support O3 OpenAI model mapping

[github-actions]

Backport of #7394 to release/4.0

/cc @tarekgh

Customer Impact

Users will be able to create a tokenizer object for the OpenAI o1 and o3 models.

Testing

Manually tested it and added a test specific to these models.

Risk

Very low. No real code change, only allow accepting the model names "o1" and "o3" to create the tokenizer instance.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Please upload report for BASE (release/4.0@208651a). Learn more about missing BASE report.

Additional details and impacted files

@@              Coverage Diff               @@
##             release/4.0    #7395   +/-   ##
==============================================
  Coverage               ?   68.89%           
==============================================
  Files                  ?     1470           
  Lines                  ?   274081           
  Branches               ?    28405           
==============================================
  Hits                   ?   188821           
  Misses                 ?    77944           
  Partials               ?     7316           

Flag	Coverage Δ
Debug	68.89% <100.00%> (?)
production	63.29% <100.00%> (?)
test	89.42% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...Microsoft.ML.Tokenizers/Model/TiktokenTokenizer.cs	78.34% <100.00%> (ø)
...est/Microsoft.ML.Tokenizers.Tests/TiktokenTests.cs	98.98% <ø> (ø)

[ericstj]

/ba-g all failures are #6978