[DEV] fix: use Stopwatch for INFO durations

[kevin-montrose]

dev targeting version of #1771

[Copilot]

Pull request overview

This PR updates Garnet’s INFO duration reporting to use a monotonic clock (Stopwatch) instead of wall-clock tick deltas, preventing negative/incorrect durations when system time changes (e.g., NTP adjustments). This aligns uptime_in_seconds and master_sync_last_io_seconds_ago with their intended “elapsed time since X” semantics.

Changes:

• Anchor server startup time using Stopwatch.GetTimestamp() and compute INFO server uptime via Stopwatch.GetElapsedTime(...).
• Track replica primary-sync “last I/O” time with Stopwatch timestamps for INFO replication (master_sync_last_io_seconds_ago).
• Add a regression test asserting uptime_in_seconds increases across successive INFO SERVER calls.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
test/Garnet.test/RespInfoTests.cs	Adds a test to validate monotonic uptime across INFO SERVER calls.
libs/server/StoreWrapper.cs	Replaces wall-clock startup ticks with a Stopwatch timestamp anchor.
libs/server/Metrics/Info/GarnetInfoMetrics.cs	Computes uptime_in_seconds / uptime_in_days using monotonic elapsed time.
libs/cluster/Server/Replication/ReplicationManager.cs	Switches replica “last primary sync I/O” duration math to monotonic time.