[Util] Introducing RoughTimestamp for second-level granularity timestamps

This timestamp type is intended to be used for invocation scheduling and the `RunAt` field of vqueues.
While it's internally represented as 4-byte integer, it'll be serialized as u63 (yes, missing one bit) in
EntryKey. This is done to allow future expansion of the granularity if needed.


The granularity is chosen to be second-level to (a) reflect the realistic expecations of invocation scheduling
and (b) to allow invocations in queues to be reordered dynamically withing a single-second window based on
their sequence ordering.

Some helpers in this type are not used (floor_to_minute, smear_to_minute) but are kept for future use if we need to
use this type for coarse jittering or if we need to expand the window-bucketing further.

Author: AhmedSoliman

Cargo.lock

@@ -17,9 +17,10 @@ restate-workspace-hack = { workspace = true }
 restate-encoding = { workspace = true }
 
 bilrost = { workspace = true }
-libc = { version = "0.2" }
 jiff = { workspace = true, optional = true }
+libc = { version = "0.2" }
 prost-types = { workspace = true, optional = true }
+rand = { workspace = true }
 schemars = { workspace = true, optional = true }
 serde = { workspace = true }
 thiserror = { workspace = true }

crates/clock/Cargo.toml

@@ -12,6 +12,7 @@
 mod hlc;
 #[cfg(feature = "test-util")]
 mod mock_clock;
+pub mod rough_ts;
 #[cfg(feature = "hlc")]
 pub mod storage;
 pub mod time;