🐛 handle MistralTokenizer special case

[prashantgupta24]

Description

Right now, MistralTokenizer doesn't support the encode_plus option. We use the encode option for now, and throw an error to the user if return_offset is requested.

Also, mistral models do NOT select mistral as the tokenizer by default. TOKENIZER_MODE=mistral has to be set in order to do that.

How Has This Been Tested?

Merge criteria:

• The commits are squashed in a cohesive manner and have meaningful messages.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 60.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 61.54%. Comparing base (44cc0d5) to head (1fc31cd).

Files with missing lines	Patch %	Lines
src/vllm_tgis_adapter/grpc/grpc_server.py	55.55%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #162      +/-   ##
==========================================
- Coverage   61.66%   61.54%   -0.13%     
==========================================
  Files          28       28              
  Lines        1693     1698       +5     
  Branches      208      210       +2     
==========================================
+ Hits         1044     1045       +1     
- Misses        553      556       +3     
- Partials       96       97       +1     

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[njhill]

Thanks @prashantgupta24, looks great just a couple of comments.

[njhill]

One last nit

[njhill]

Thanks @prashantgupta24!