Function parse_level_directive 

pub fn parse_level_directive(raw: &str) -> Option<LevelFilter>

Map a caller-supplied verbosity spelling onto a LevelFilter. Wraps the internal [parse_log_level] for out-of-crate callers (the CLI --log-level flag, the Python set_log_level shim). Returns None for blank/unrecognized input so the caller decides the fallback rather than guessing here.