Add SM120 shared memory guards for tile selection

[ivandobskygithub]

Summary

• add explicit shared-memory estimator and clamping to the SM90 tile selector to respect the SM120 limit
• compile a small bridge for tile_size_fwd_sm90 and exercise head/value/paging permutations under the SMEM cap

Testing

• pytest tests/hopper/test_tile_size_shared_memory.py -q

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Codex Task