test: add coverage for mql/errors/types/utils/health (currently zero)

[Lutherwaves]

Check Existing Issues

• I have searched the existing issues and discussions.

Problem Description

Several packages have zero test coverage, so regressions in them are invisible:

• mql/ (expr.go, parser.go) — no tests, and it currently has real correctness bugs (see the wildcard/IN issue). Highest priority.
• errors/errors.go — no tests for StatusCode() / Error() across the error types.
• types/types.go — no tests for GetOpenAPIDefinitions / MergeOpenAPIDefinitions.
• utils/utils.go — no tests for NewId() / id conversion.
• health/health.go — no tests for storage + dependency check paths.

Desired Solution you'd like

Add focused unit tests for each package above. Suggested order by value:

1. mql/ — parser edge cases (empty input, unmatched parens, empty lists, escaped quotes) and expr evaluation (AND/OR/NOT/group, all operators, wildcard segments, IN case sensitivity). This also locks in the fix for the wildcard/IN bug.
2. errors/ — table test asserting each type's status code and message.
3. health/, types/, utils/ — happy path + error/edge cases.

Additional Context

Found during a general audit of the library. Marked good first issue — each package is small and self-contained, ideal for newcomers. The mql/ portion is best paired with the wildcard bug fix.