[REFACTOR] refactor unit tests

[mayank31398]

No description provided.

[gemini-code-assist]

Code Review

This pull request restructures the test suite by moving multi-GPU and other tests out of nested subdirectories to the root tests directory, updating relative imports and module paths accordingly. It also introduces a conftest.py file to ensure multi-GPU tests run before single-GPU tests to prevent CUDA context conflicts. The reviewer suggested optimizing the test collection modification logic in conftest.py to partition the tests in a single O(N) pass instead of performing redundant set allocations inside a list comprehension.

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[gemini-code-assist]

In the current implementation, set(multi_gpu) is evaluated inside the list comprehension for every single item in items. This results in an $O(N^2)$ complexity and redundant set allocations.

We can optimize this to a single $O(N)$ pass by iterating through items once and partitioning them into two lists directly.

Suggested change

	def pytest_collection_modifyitems(items: list) -> None:
	multi_gpu = [i for i in items if any(p in _MULTI_GPU_DIRS for p in i.nodeid.split("/"))]
	other = [i for i in items if i not in set(multi_gpu)]
	items[:] = multi_gpu + other
	def pytest_collection_modifyitems(items: list) -> None:
	multi_gpu = []
	other = []
	for item in items:
	if any(p in _MULTI_GPU_DIRS for p in item.nodeid.split("/")):
	multi_gpu.append(item)
	else:
	other.append(item)
	items[:] = multi_gpu + other