Add stable env DeviceSegmentedSort::Pairs 1/2

[gonidelis]

fixes #7551

Follows exactly same logic as #8002

Let's merge it after this one ^^^

[NaderAlAwar]

Important: can we add one representative MR/temp-storage env test here too? At the moment this only checks stream propagation, but these APIs also go through dispatch_with_env, so the memory-resource path is currently untested.

[gonidelis]

@NaderAlAwar isn't the mr tested by default in lid_2 here?

cccl/cub/test/catch2_test_env_launch_helper.h

Lines 466 to 467 in e1a7506

	auto mr = device_memory_resource{{}, stream, &bytes_allocated, &bytes_deallocated};
	auto mr_env = cuda::std::execution::prop{cuda::mr::__get_memory_resource_t{}, mr};

[NaderAlAwar]

That MR coverage exists for the DECLARE_LAUNCH_WRAPPER / TEST_LAUNCH path, but this file explicitly does not use that path, so it doesn’t apply here. This means that there is no lid_2 variant here.

[NaderAlAwar]

Actually wait, I was wrong, I saw an older version of the PR, we do have DECLARE_LAUNCH_WRAPPER here. I still think we should not use lid_2 for similar reasons to here #8286 (comment)

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