[SIMT][OPT] Add persistent SIMT fragment materialization

[KurrinQu]

Summary

Add PTOAS support for keeping SIMT fragment values in dedicated register
slots across multiple inline SIMT sections.

The transformation replaces repeated UB-to-register loads with explicit
pto.keep / pto.resume traffic while preserving the existing VPTO lowering
and outlining flow.

Changes

• Add a read-only persistent-fragment analysis pass.
• Add the persistent-fragment materialization pass.
• Keep inline SIMT sections until persistent-fragment materialization completes,
  then outline them into pto.simt_entry helpers and pto.simt_launch calls.
• Add positive and negative lit coverage for access normalization, slot
  assignment, vector accesses, control-flow contracts, invalid offsets,
  launch-dimension mismatches, and slot-budget violations.

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.