[DOCS] Document Python FFI conversion protocols

[tqchen]

This documents the Python argument conversion protocols recognized when calling TVM-FFI functions.

Summary:

• Add a Python guide subsection for argument conversion protocols.
• Document the supported __tvm_ffi_* hooks and __cuda_stream__ in a protocol table.
• Point DLPack-compatible objects to the DLPack protocol documentation.
• Add a cross-reference from the Function and Module concept page.

Validation:

• pre-commit run --files docs/guides/python_lang_guide.md docs/concepts/func_module.rst
• uv run --group docs sphinx-build -M html docs docs/_build

[gemini-code-assist]

Code Review

This pull request adds comprehensive documentation for Python argument conversion protocols in TVM FFI, explaining how Python values are converted to the FFI Any calling convention and detailing various special protocol hooks (such as __tvm_ffi_object__, __tvm_ffi_value__, and __cuda_stream__). A review comment points out a misleading description in the documentation table for the __cuda_stream__(self) protocol, suggesting it should be corrected to clarify that it returns an integer stream pointer rather than a protocol object.

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