[Feature][Codegen] Remove the legacy Text SunMMIO backend path and Refocus SunMMIO skeleton tests on traversal coverage completeness

[firefrogliu666]

PR Summary

This PR has two main goals:

• Remove the legacy Text SunMMIO backend path
• Refocus SunMMIO skeleton tests on traversal coverage completeness

1) Text backend removal (SUVM-only path)

• Removes TextSunMMIOBuilder and its text-specific code path.
• Removes backend selection plumbing (text vs suvm) from SunMMIO codegen/runtime integration.
• Makes target.build.tilelang_sunmmio_without_compile use SUVM path only (with backend validation/default behavior aligned to SUVM).
• Keeps builder abstraction in place (no broad architecture refactor).

2) Skeleton test refocus

• Reworks testing/python/target/test_sunmmio_codegen_skeleton.py to make coverage report the primary oracle for codegen_sunmmio.cc traversal.
• Keeps minimal smoke/failure tests (non-empty source, While/Shuffle unsupported, compile-path not implemented).
• Removes brittle text-format assertions.
• Keeps synthetic coverage kernels and adds a real TileLang frontend kernel in coverage parameterization.

Coverage Oracle

• Uses:
  • TL_SUNMMIO_CODEGEN_COVERAGE_PATH
  • TL_SUNMMIO_CODEGEN_COVERAGE_STRICT=1
• Asserts:
  • report exists
  • required keys exist
  • missing_node_types == []
  • missing_call_ops == []

Validation

• Ran:
  • PYTHONPATH=/home/liuchunfeng/Tilelang-Mesh-Sync-Pc/python:/home/liuchunfeng/Tilelang-Mesh-Sync-Pc /home/liuchunfeng/.conda/envs/tl/bin/python -m pytest -q testing/python/target/test_sunmmio_codegen_skeleton.py
• Result:
  • 8 passed