Add type hints for router methods meta kwargs

[flapili]

Pull Request

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What’s Included?

• New feature
• Bug fix
• Documentation improvement
• Refactor / internal change

Describe your changes:
Adding type hint to document usage of router's methods like get/post/... to help autocompletion, does not change runtime behavior

For now the code is draft, contains TODOs and I was not sure where I should put the Meta class so in the meantime, I nested it in the router 👀

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How Was It Tested?

For now only checking autocompletion & docstring work in editor (I noticed that Ty lsp does not handle fields docstrings in typedDict yet(?) but pylance do work)

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Anything Else?

Optional:

• Any TODOs or follow-up items?

• Where Meta should be located?
• check sys.version_info to import Unpack & NotRequired for 3.11 & 3.12 respectivly ?

• Known limitations or trade-offs?
• Anything you'd like reviewers to focus on?

• I'm not sure about how to word docstrings properly

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