[ayushmishra2005]

Closes #1757

Intent

• Allow sig-lint to run against specific files or directories instead of relying only on paths defined in source.
• Preserve the existing full-project lint behavior when no custom paths are supplied.

Implementation

• Added repeatable --path <path> arguments.

  zig build lint -- --path tools/lint
  zig build lint -- --path tools/lint --path v2/lib
  

• Explicit paths replace the default project paths for that run.
• Directories are scanned recursively, while explicit files must be Zig source files.
• Paths are resolved relative to the repository root and normalized before collection.
• Duplicate and overlapping inputs are deduplicated before files are parsed.
• Scoped runs only validate relevant line-length exclusions and test-inclusion roots.
• Exact-file runs apply file-level rules without triggering directory-level test-inclusion checks.
• The lint run step now uses the repository root as its working directory.
• Updated the README with the new usage.

Test

Validated with Zig 0.15.2:

zig fmt --check build.zig tools/lint
zig build lint
zig build lint -- --help
zig build lint -- --path tools/lint/main.zig
zig build lint -- --verbose --path tools/lint --path v2/lib