CBG-5453: [4.0.6 backport] generate HLV.version from our own HLC for SGW actor writes

[gregns1]

CBG-5453

Backports #8355

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Dependencies (if applicable)

• Link upstream PRs
• Update Go module dependencies when merged

Integration Tests

• https://jenkins.sgwdev.com/job/SyncGatewayIntegration/810/

[Copilot]

Pull request overview

Backport to generate HLV current-version values from a Sync Gateway–owned Hybrid Logical Clock (HLC) for SG actor writes, avoiding server-side CAS macro expansion for _vv.ver and adding safety logic to preserve the cv.ver <= cas invariant needed for XDCR.

Changes:

• Introduce base.HybridLogicalClock and store one per DatabaseContext to generate literal HLV version values for SG writes and merge resolution.
• Add post-write correction (correctVersionAheadOfCAS) that re-stamps CAS when a generated HLV version ends up ahead of the committed CAS (bounded wait + new internal stat).
• Update/extend unit + integration tests to assert on HLV version semantics (not equality with CAS) and add coverage for many channel removals; temporarily skip topology tests on Windows.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
topologytest/main_test.go	Skips topology tests on Windows due to non-deterministic HLV ordering from low clock precision.
rest/replicatortest/replicator_test.go	Updates replicator conflict assertions to expect HLV versions not equal to CAS.
rest/replicatortest/replicator_conflict_test.go	Adjusts conflict setup/expectations to use HLC-generated versions for local/remote HLV edits.
rest/changes_test.go	Changes CV assertions to compare against doc.HLV.Version instead of doc.Cas.
rest/blip_api_crud_test.go	Adds coverage for many channel removals on doc updates; removes long-channel-name macro-expansion test path.
rest/api_test.go	Updates REST API tests to validate HLV version semantics (!= 0, <= CAS) and adds many-channel-removal coverage.
db/utilities_hlv_testing.go	Makes test HLV agent explicitly simulate external peers macro-expanding both _vv.ver and _vv.cvCas; adds HLC test accessor.
db/revision_cache_test.go	Updates channel update call signature and expected CV to use doc.HLV.Version.
db/hybrid_logical_vector.go	Adds maxValueForSource helper and removes macro-expansion plumbing for _vv.ver / channel revocation paths.
db/hybrid_logical_vector_test.go	Adds tests for CAS-ahead correction behavior and maxValueForSource.
db/document.go	Simplifies updateChannels signature (removes revoked-channel macro-expansion tracking).
db/database.go	Adds hlc to DatabaseContext and initializes it in NewDatabaseContext; updates call sites for updateChannels.
db/database_test.go	Updates resync expectations to use preResyncDoc.HLV.Version rather than CAS.
db/crud.go	Generates HLV versions via db HLC, writes literal _vv.ver, adds post-write CAS re-stamp correction + helper to re-persist xattrs.
db/crud_test.go	Updates tests to no longer assume HLV.Version == CAS and removes revoked-channel-path tests.
db/changes_test.go	Updates changes/CV tests to assert CV values against doc.HLV.Version.
base/stats.go	Adds internal counter stat hlv_version_cas_retry_count and version constant 4.0.6.
base/stats_descriptions.go	Adds description string for hlv_version_cas_retry_count.
base/hlc.go	Introduces HybridLogicalClock used to generate CAS-comparable, monotonic HLV version values.
base/hlc_test.go	Adds unit tests for HLC monotonicity, floor behavior, masking, and concurrency.