[codex] Extend A5 PTODSL micro coverage

[zhoubot]

Summary

• extend the A5 PTODSL micro-backed tile library with indexed, select, and remaining reduction coverage
• add TGatherB, TScatter, TExpandS, TPrelu, TSel, and TSels implementations plus generated tile-op PTO examples
• refresh the A5 coverage manifests and regression suite to track the expanded micro coverage

What changed

• added new A5 modules:
  • ptodsl/lib/a5/tindex.py
  • ptodsl/lib/a5/tselect.py
• extended existing A5 micro rewrites in:
  • ptodsl/lib/a5/tbinary.py
  • ptodsl/lib/a5/treduce.py
  • ptodsl/lib/a5/tscalar.py
  • ptodsl/lib/a5/tsort.py
  • ptodsl/lib/a5/tile_op_kernels.py
• updated the public A5 surface and validation helpers in:
  • ptodsl/lib/a5/ops.py
  • ptodsl/lib/a5/__init__.py
  • ptodsl/lib/a5/_common.py
• regenerated coverage and tile-op artifacts:
  • ptodsl/lib/a5/A5_HEADER_COVERAGE.md
  • ptodsl/lib/a5/TILE_MICRO_CHECKLIST.md
  • ptodsl/lib/a5/generated/tile_ops/*
• expanded regression coverage for the new micro-backed ops

Validation

PYTHONPATH=/Users/zhoubot/github/.llvm-19.1.7/build-mlir-py312/tools/mlir/python_packages/mlir_core:/Users/zhoubot/github/pto-org/PTOAS/install-src312:/Users/zhoubot/github/pto-org/PTOAS/build-src312/python \
/Users/zhoubot/github/.venv-ptoas-src312/bin/python -m pytest -q \
  tests/regression/test_a5_lib_regression.py \
  tests/regression/test_tile_micro_coverage.py \
  tests/regression/test_a5_header_coverage.py \
  tests/regression/test_generated_tile_op_pto.py

Result: 66 passed in 1.04s