[GPUHeuristics] Refactor MMA heuristic seeds to be architecture-specific (#23717)

Each GPU architecture now defines a constexpr ArchSeedSet containing
gemm, scaled gemm, and convolution seed arrays indexed by GemmSize. The
architecture is determined from the target and the corresponding seed
set is returned (e.g. RDNA4 uses tuned seeds from RX 9070 XT
benchmarking, others use the default). GemmSize enum values are changed
to start at 0 for direct array indexing.

Add RDNA4 (gfx1201) config tests covering small, medium, and large
matmul and convolution shapes.

RDNA4 benchmark results (RX 9070 XT, vs default seeds):
- GEMM shapes: ~40% of shapes improved, 15.9% geometric mean speedup.
- Prod Conv shapes: ~25% of shapes improved, 6% geometric mean speedup.
- Proxy Conv shapes: ~30% of shapes improved, 14.5% geometric mean
speedup.

---------

Signed-off-by: yzhang93 <zhyuhang88@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>