Macro log 

macro_rules! log {
    ($level:expr, $fmt:expr) => { ... };
    ($level:expr, $fmt:expr, $($arg:tt)*) => { ... };
    ($fmt:expr) => { ... };
    ($fmt:expr, $($arg:tt)*) => { ... };
    (@inner $level:expr, $fmt:expr, $($arg:tt)*) => { ... };
}

Emit a structured log line with consistent coloring and headers.

Accepts an optional Log level followed by a format string and arguments, mirroring format!. When the level is omitted the macro defaults to Log::Debug.