fix(extract timestamp_checked_add as lib) (#10383)

* fix(extract `timestamp_checked_add` as lib)

* fix(whisper types): remove unused `EmptyTopics`

* fix(time-lib): feature-flag to use time-lib or std

This commit adds conditional compilation checks that falls back to `our time-lib` when
`time_checked_add` is not available in the standard library

Note, `time_checked_add` covers both `checked_add` and `checked_sub`

* fix(grumble): use cfg_attr to define rustc feature

util/time-utils/src/lib.rs

@@ -0,0 +1,50 @@
+use std::time::{Duration, SystemTime, UNIX_EPOCH};
+
+/// Temporary trait for `checked operations` on SystemTime until these are available in standard library
+pub trait CheckedSystemTime {
+	/// Returns `Some<SystemTime>` when the result less or equal to `i32::max_value` to prevent `SystemTime` to panic because
+	/// it is platform specific, possible representations are i32, i64, u64 and Duration. `None` otherwise
+	fn checked_add(self, _d: Duration) -> Option<SystemTime>;
+	/// Returns `Some<SystemTime>` when the result is successful and `None` when it is not
+	fn checked_sub(self, _d: Duration) -> Option<SystemTime>;
+}
+
+impl CheckedSystemTime for SystemTime {
+	fn checked_add(self, dur: Duration) -> Option<SystemTime> {
+		let this_dur = self.duration_since(UNIX_EPOCH).ok()?;
+		let total_time = this_dur.checked_add(dur)?;
+
+		if total_time.as_secs() <= i32::max_value() as u64 {
+			Some(self + dur)
+		} else {
+			None
+		}
+	}
+
+	fn checked_sub(self, dur: Duration) -> Option<SystemTime> {
+		let this_dur = self.duration_since(UNIX_EPOCH).ok()?;
+		let total_time = this_dur.checked_sub(dur)?;
+
+		if total_time.as_secs() <= i32::max_value() as u64 {
+			Some(self - dur)
+		} else {
+			None
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn it_works() {
+		use super::CheckedSystemTime;
+		use std::time::{Duration, SystemTime, UNIX_EPOCH};
+
+		assert!(CheckedSystemTime::checked_add(UNIX_EPOCH, Duration::new(i32::max_value() as u64 + 1, 0)).is_none());
+		assert!(CheckedSystemTime::checked_add(UNIX_EPOCH, Duration::new(i32::max_value() as u64, 0)).is_some());
+		assert!(CheckedSystemTime::checked_add(UNIX_EPOCH, Duration::new(i32::max_value() as u64 - 1, 1_000_000_000)).is_some());
+
+		assert!(CheckedSystemTime::checked_sub(UNIX_EPOCH, Duration::from_secs(120)).is_none());
+		assert!(CheckedSystemTime::checked_sub(SystemTime::now(), Duration::from_secs(1000)).is_some());
+	}
+}