Skip log formatting entirely for DevNull output

Even though DevNull discards the bytes, the formatting work
(SubstringFormatter, fmt::write, from_utf8) was still being done
on every log call. Short-circuit in TestLogger::log via a TypeId
check, which monomorphization resolves at compile time.

AI tools were used in preparing this commit.

Author: joostjager

fuzz/src/utils/test_logger.rs

@@ -8,6 +8,7 @@
 // licenses.
 
 use lightning::util::logger::{Logger, Record};
+use std::any::TypeId;
 use std::io::Write;
 use std::sync::{Arc, Mutex};
 
@@ -66,6 +67,9 @@ impl<'a, Out: Output> Write for LockedWriteAdapter<'a, Out> {
 
 impl<Out: Output> Logger for TestLogger<Out> {
 	fn log(&self, record: Record) {
+		if TypeId::of::<Out>() == TypeId::of::<DevNull>() {
+			return;
+		}
 		writeln!(LockedWriteAdapter(&self.out), "{:<6} {}", self.id, record).unwrap();
 	}
 }