CBG-5460 move hlc implementation to sg-bucket

[torcolvin]

This review was already done in an earlier stage of couchbase/sync_gateway#8375 - this just collapses the code into the sg-bucket repo from the sync_gateway and rosmar repos. This moves hlc files into sg-bucket from sync_gateway as they were done in the upstream sync gateway PR.

Blocks couchbaselabs/rosmar#79 and couchbase/sync_gateway#8375

[Copilot]

Pull request overview

This PR introduces a Hybrid Logical Clock (HLC) implementation into the sg-bucket module (moved from Sync Gateway / Rosmar), including platform-specific wall-clock handling and accompanying unit tests.

Changes:

• Added HybridLogicalClock implementation for generating CAS-comparable HLC timestamps.
• Added Windows-specific high-resolution wall clock implementation (via GetSystemTimePreciseAsFileTime) with a non-Windows fallback.
• Added unit tests covering monotonicity, masking, flooring behavior, reverse-time behavior, and concurrency safety; updated module dependencies to include golang.org/x/sys.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
hlc.go	Core HLC implementation and exported helpers/constants.
hlc_nonwindows.go	Non-Windows wall-clock source using time.Now().UnixNano().
hlc_windows.go	Windows wall-clock source using high-resolution system time.
hlc_test.go	Test suite for HLC correctness and concurrency behavior.
go.mod	Adds golang.org/x/sys and bumps Go version directive.
go.sum	Adds checksums for the new golang.org/x/sys dependency.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.