fix(tools): restrict legacy platform metadata check to wave-test directives

[Visio-Vanitas]

Summary

Restrict the legacy platform metadata validation in tools/case_manifest.py (_validate_case_layout) so that host-os= and host-arch= are only matched inside actual leading // wave-test: directives rather than across arbitrary source file contents.

Motivation

Fixes #583. Previously, _validate_case_layout searched the entire Wave source text for substring matches of host-os= and host-arch=. This caused legitimate cases containing these strings in code literals or normal comments to be falsely rejected as legacy metadata.

Target and compatibility impact

None. Tooling validation only; does not affect compiler or runtime targets.

Validation

• Added unit tests in tools/test_case_manifest.py verifying:
  • Cases with host-os= or host-arch= in string literals and ordinary comments pass layout validation.
  • Directives with deprecated keys (host-os=, host-arch=, with or without whitespace, standalone or comma-separated) are rejected with CaseManifestError.
• Ran python3 -m unittest tools.test_case_manifest tools.test_test_contracts: all 23 tests passed.
• Ran python3 -m unittest discover tools: all 40 tests passed.

Checklist

• Commits include a DCO Signed-off-by line.
• Tests cover new behavior or the PR explains why no test is needed.
• User-facing changes include documentation or diagnostics updates.
• The change preserves the license boundary between the compiler and std/.

[LunaStev]

LGTM. Thanks for the contribution! I’ll merge this once all CI checks have completed.