Turn Taskless Rust rules into a low-noise failing gate

[arniber21]

What to build

Make the repository's Taskless rules enforce production invariants instead of returning success with hundreds of warnings from unit tests embedded in source modules.

Acceptance criteria

• Unwrap/expect matching excludes code nested beneath cfg(test) as well as test directories.
• Production violations of error-handling and wire-DTO rules fail Taskless CI.
• Existing production findings are resolved or explicitly scoped with narrow justified exceptions.
• Rule tests cover production code, integration tests, and in-source unit-test modules.
• A full scan produces no irrelevant unit-test warnings.

Blocked by

None - can start immediately.

[arniber21]

Implemented and merged via PR #449. Closing as complete.