Refactor test_mla_v1.py to reduce redundant @patch decorators

[zzhx1]

What this PR does / why we need it?

This PR refactors test_mla_v1.py to eliminate redundant @patch decorators across multiple test classes

• vLLM version: v0.11.2
• vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

[github-actions]

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[gemini-code-assist]

Code Review

This pull request effectively refactors the tests in test_mla_v1.py by introducing a pytest fixture to consolidate numerous repeated @patch decorators. This significantly reduces code duplication and improves the maintainability of the test suite. The implementation is solid, but I've identified a few instances where the new fixture is requested redundantly in test methods, which I've commented on. Addressing these will make the refactoring even cleaner.

[gemini-code-assist]

The mock_distributed fixture is unused in this test method and can be removed. The setUp method already requests this fixture, which ensures that the necessary patches are active for the duration of the test. Including it here is redundant and can be misleading.

Suggested change

	**kwargs)
	def test_init(self):

[gemini-code-assist]

The mock_distributed fixture is unused in this test method and can be removed. The setUp method already requests this fixture, which ensures that the necessary patches are active for the duration of the test. Including it here is redundant.

Suggested change

	self.assertEqual(self.impl.tp_size, 2)
	def test_q_proj_and_k_up_proj(self):

[gemini-code-assist]

The mock_distributed fixture is unused in this test method and can be removed. The setUp method already requests this fixture, which ensures that the necessary patches are active for the duration of the test. Including it here is redundant.

Suggested change

	self.assertEqual(self.impl.W_UV.shape[2], self.impl.v_head_dim)
	def test_compute_prefill_context_none(self):

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.