[Docs] Add API reference for tvm.arith, tvm.testing, tvm.exec, tvm.tirx.backend and extend topi/contrib/ir/target docs

[tlopex]

as per title

[gemini-code-assist]

Code Review

This pull request expands the Python API documentation by adding several new modules and sub-modules, including tvm.arith, tvm.exec, tvm.testing, and various components within contrib, ir, target, tirx, and topi. Feedback focuses on maintaining alphabetical order in the main index and ensuring consistent heading styles and non-redundant titles in the newly created documentation files.

[gemini-code-assist]

The module arith is inserted out of alphabetical order. For better maintainability and navigation, the toctree entries should be sorted alphabetically (e.g., arith should be the first entry in this list).

[gemini-code-assist]

These entries are not sorted alphabetically. exec should come before testing.

Suggested change

	testing
	exec
	exec
	testing

[gemini-code-assist]

The module tirx/backend is added at the end of the list, which breaks the alphabetical order. It should ideally follow tirx/analysis.

[gemini-code-assist]

The heading style in this file is inconsistent with other API reference files in this directory (which typically use - for the main title and ~ for sub-sections). Additionally, the title tvm.tirx.backend is redundant as it appears twice.

Please ensure the underline length matches the title length exactly.

Suggested change

	tvm.tirx.backend
	================
	tvm.tirx.backend
	*****************
	.. automodule:: tvm.tirx.backend
	:members:
	:imported-members:
	tvm.tirx.backend.adreno
	***********************
	.. automodule:: tvm.tirx.backend.adreno
	:members:
	:imported-members:
	tvm.tirx.backend
	----------------
	.. automodule:: tvm.tirx.backend
	:members:
	:imported-members:
	tvm.tirx.backend.adreno
	~~~~~~~~~~~~~~~~~~~~~~~
	.. automodule:: tvm.tirx.backend.adreno
	:members:
	:imported-members: