Enable Pydantic mypy checks and convert configs to Pydantic dataclasses

[hmellor]

• Enables the mypy extension for Pydantic
• Fix the new mypy errors created by doing that
• Swap out the builtin dataclasses for Pydantic dataclasses (free input validation!)

  $ vllm serve meta-llama/Llama-3.2-1B-Instruct --gpu-memory-utilization 0.45 --compilation-config '{"level":2.5}'
  INFO 05-12 12:59:58 [__init__.py:248] Automatically detected platform cuda.
  WARNING 05-12 13:00:02 [config.py:2034] max_model_len was is not set. Defaulting to arbitrary value of 8192.
  WARNING 05-12 13:00:02 [config.py:2040] max_num_seqs was is not set. Defaulting to arbitrary value of 128.
  usage: vllm serve [model_tag] [options]
  vllm serve: error: argument --compilation-config/-O: 1 validation error for CompilationConfig
  level
    Input should be a valid integer, got a number with a fractional part [type=int_from_float, input_value=2.5, input_type=float]
      For further information visit https://errors.pydantic.dev/2.11/v/int_from_float

N.B. Pydantic base models handle mutable defaults correctly. x: list = [] looks much nicer than the alternative mypy will allow x: list = Field(default_factory=lambda: [])

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[hmellor]

I think this PR must wait for #17485. Hopefully the switch to static analysis in the docs build will prevent the Pydantic errors

[russellb]

thanks!

[russellb]

well, I'm happy with the changes in general, but it looks like you have some failing tests.

dismissing approval, pending test resolution

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @hmellor.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @hmellor.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[hmellor]

Instead of fighting Sphinx, I will try and merge #18145 so that we never have to think about breaking the docs build again 🎉

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @hmellor.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork