test(parsers): add config_registry drift guard

[speriaswamy-amd]

Part 14 of 14 in a stack for AIMVT-276.
Base: #346.

Why

Nothing previously enforced that cvs man's registry (config_registry.py)
stays in sync with the pydantic schemas and shipped sample configs. Without
a guard, a schema field could go undocumented, a sample could drift out of
sync with its schema, or a stripped _comment_*/_example_* key could
silently creep back in — and nobody would notice until a customer hit it.

What changed

• Added cvs/parsers/unittests/test_config_registry.py, asserting for
  every suite in TEST_CONFIG_DOCS:
  • its declared sample paths exist on disk
  • its test name is a real, discoverable test suite
  • every schema parameter has a non-empty description
  • every suite has a summary
  • its shipped samples validate against their schema
  • every key in a shipped sample maps to a declared schema field (with one
    tracked exception: rccl_config.json's root-level results block,
    which rccl_lib.py never reads from that location — a pre-existing
    functional quirk, not something to paper over by mis-documenting it)
  • the four pilot suites' migrated samples carry no leftover
    _comment_*/_example_* documentation keys