clippy lint in Instant::duration_since

Fixes a new CI error in Rust 1.94:

error: manual saturating arithmetic
  --> src/time/instant.rs:33:30
   |
33 |         Duration::from_nanos(self.0.checked_sub(earlier.0).unwrap_or_default())
   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `saturating_sub`: `self.0.saturating_sub(earlier.0)`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.94.0/index.html#manual_saturating_arithmetic
   = note: `-D clippy::manual-saturating-arithmetic` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::manual_saturating_arithmetic)]`

Author: pchickey

src/time/instant.rs

@@ -30,7 +30,7 @@ impl Instant {
     /// Returns the amount of time elapsed from another instant to this one, or zero duration if
     /// that instant is later than this one.
     pub fn duration_since(&self, earlier: Instant) -> Duration {
-        Duration::from_nanos(self.0.checked_sub(earlier.0).unwrap_or_default())
+        Duration::from_nanos(self.0.saturating_sub(earlier.0))
     }
 
     /// Returns the amount of time elapsed since this instant.