Mark get_log_level() pure for consistency and optimization #1347
Description
Rationale
- get_log_level() only returns a module variable and has no side effects.
- Marking it pure clarifies intent, enables compiler optimizations, and documents API guarantees.
- Aligns with project Fortran guidelines: prefer purity; mark pure/elemental when applicable.
Scope
- Update src/external/fortplot_logging.f90: declare get_log_level as pure.
- No behavior change; existing tests cover correctness of returned level.
Risk
- Very low. No I/O or global mutation in the function; signature remains the same.
Verification
- Run make test and make test-ci; no regressions expected.