[FIX][Relax] Validate DeviceMesh cardinality without overflow - #20346
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Share checked int64 shape multiplication across both constructors and validate ranges before generating device IDs. Preserve zero-dimension and empty-shape semantics.
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Fixes #20272.
Use a checked 64-bit shape product in both
DeviceMeshconstructors. Reject negative dimensions and overflow without narrowing the device count. Validate constant Range bounds and cardinality before generating IDs, and avoid overflowing the final ID.Preserve empty-shape and zero-dimension product semantics. This does not change duplicate-ID policy.
Validation on Linux CPU / LLVM 16 (
cc0f9f07, pinned TVM FFI): the original code incorrectly accepted 10 invalid-cardinality cases; after this change the complete DTensor-type test file reports 25 passed. Coverage includes both constructors, ordinary mismatches, 32/64-bit overflow, negative/zero dimensions, nonconstant ranges, and large starting IDs. Large-shape cases use empty lists or short ranges, not large allocations.Changed-file pre-commit checks passed. No GPU tests run.