fix(ci): remove useless unsigned comparison in timing tests

Remove useless comparison `time.as_millis() >= 0` in timing test.
Since `as_millis()` returns u128 (unsigned), the comparison is
always true and triggers `-D unused-comparisons` in CI.

The test already validates upper bound with `<= 15` check, which
is sufficient to ensure the traffic shaper timing is reasonable.

Fixes CI failure on main branch.

Author: doublegate

crates/wraith-obfuscation/src/timing.rs

@@ -419,7 +419,6 @@ mod tests {
         let time = shaper.time_until_next();
 
         // Should be close to 10ms (1000ms / 100 pps)
-        assert!(time.as_millis() >= 0);
         assert!(time.as_millis() <= 15);
     }