Add bench-exchange tx send metrics (#3890)

sdk/src/timing.rs

@@ -24,6 +24,10 @@ pub const MAX_HASH_AGE_IN_SECONDS: usize = 120;
 // This must be <= MAX_HASH_AGE_IN_SECONDS, otherwise there's risk for DuplicateSignature errors
 pub const MAX_RECENT_BLOCKHASHES: usize = MAX_HASH_AGE_IN_SECONDS;
 
+pub fn duration_as_ns(d: &Duration) -> u64 {
+    d.as_secs() * 1_000_000_000 + u64::from(d.subsec_nanos())
+}
+
 pub fn duration_as_us(d: &Duration) -> u64 {
     (d.as_secs() * 1000 * 1000) + (u64::from(d.subsec_nanos()) / 1_000)
 }