feat(watch): implement --debounce flag with duration (#16187)

- fixes #16178
- `watch --debounce-ms` deprecated

Co-authored-by: Luca Scherzer <luca.scherzer@de.clara.net>

crates/nu-protocol/src/value/mod.rs

@@ -89,6 +89,7 @@ pub enum Value {
         internal_span: Span,
     },
     Duration {
+        /// The duration in nanoseconds.
         val: i64,
         /// note: spans are being refactored out of Value
         /// please use .span() instead of matching this span value