fix(pto): infer matmul tile config by target arch

[HecreReed]

Summary

• add a dedicated pto-infer-tile-config pass that derives LEFT/RIGHT/ACC tile config from pto.target_arch
• run the pass before PTOViewToMemref so emitted pointer_cast/bind_tile metadata matches the target ISA on both A3 and A5
• add A3/A5 regression tests as .pto inputs that lock the generated Tile<...> templates for matmul operands/results

Why

• PTO-ISA expects different canonical LEFT tile layout on A3 vs A5, while RIGHT/ACC also need fixed fractal/layout combinations
• keeping this inference in PTO IR removes the need for users to hand-thread BLayout/SLayout into matmul tiles
• this also prevents low-level lowering from carrying stale default configs into generated C++

Testing

• ninja -C build-llvm19 ptoas
• build-llvm19/tools/ptoas/ptoas --pto-arch=a3 test/basic/matmul_tile_config_infer_a3.pto | /opt/homebrew/opt/llvm@19/bin/FileCheck test/basic/matmul_tile_config_infer_a3.pto
• build-llvm19/tools/ptoas/ptoas --pto-arch=a5 test/basic/matmul_tile_config_infer_a5.pto | /opt/homebrew/opt/llvm@19/bin/FileCheck test/basic/matmul_tile_config_infer_a5.pto