Fix NvDec decoder stale state when cropping

[mthrok]

This commit address an issue where executing test_nvdec_decode_crop_resize before test_nvdec_decode_h264_420p_crop causes the latter to return wrong results
due to bad state left behind.

The fix involves modifying the NvDecDecoderCore::reset() method to properly clean up state,
including resetting crop, target width and height, and source information to default values.
This ensures that the thread-local cached decoder does not carry over stale parameters from previous test runs.

Modifying the NvDecDecoderCore is more elaborated, so, for now, we disable cache if crop is provided.

This commit also adds the stand alone test that would repro the issue without the patch.
Moved to #1186 as the test manifests a different issue.

• w/o fix https://github.com/facebookresearch/spdl/actions/runs/19650268816
• w/ fix https://github.com/facebookresearch/spdl/actions/runs/19641739313

Closes #1159

[meta-codesync]

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