[Util] Introducing RoughTimestamp for second-level granularity timestamps

[AhmedSoliman]

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.

---

Stack created with Sapling. Best reviewed with ReviewStack.

• [VQueues] Introduce sys_vqueue_stats datafusion table #4580
• [VQueues] Update VQueueStatistics after transitions #4574
• [VQueues] Keys redesigned to support scheduler-driven retries #4573
• New VQueueId #4565
• Remove num_tokens_used from VQueueMeta #4564
• Introduces independent lock storage and vqueue scheduler resource manager #4563 (2 commits)
• Introducing locks table #4562
• Use state mutation ID in vqueues #4570
• Support for partitioned identifiers + state mutation request id #4569
• -> [Util] Introducing RoughTimestamp for second-level granularity timestamps #4572

[github-actions]

Test Results

  7 files   -  1    7 suites   - 1   5m 3s ⏱️ + 2m 25s
 49 tests  -  4   49 ✅  -  4  0 💤 ±0  0 ❌ ±0 
210 runs   - 23  210 ✅  - 23  0 💤 ±0  0 ❌ ±0 

Results for commit 701c5d7. ± Comparison against base commit 5560b2f.

This pull request removes 4 tests.

dev.restate.sdktesting.tests.UserErrors ‑ failSeveralTimesWithMetadata(URI)
dev.restate.sdktesting.tests.UserErrors ‑ internalCallFailurePropagationWithMetadata(URI)
dev.restate.sdktesting.tests.UserErrors ‑ invokeTerminallyFailingCallWithMetadata(URI)
dev.restate.sdktesting.tests.UserErrors ‑ sideEffectWithTerminalErrorWithMetadata(URI)

♻️ This comment has been updated with latest results.