fix(leader-election): validate lease duration conversions

[GatewayJ]

Type of Change

• New Feature
• Bug Fix
• Documentation
• Performance Improvement
• Test/CI
• Refactor
• Other: N/A

Related Issues

Closes rustfs/backlog#1081

Summary of Changes

• Validate configured lease durations before serializing them into the Kubernetes int32 seconds field.
• Re-check timing invariants using the persisted whole-second duration.
• Centralize lease validity evaluation so non-positive durations expire without unchecked casts or panicking date arithmetic.
• Treat date-range overflow conservatively as still valid to preserve mutual exclusion.
• Add unit and integration coverage for negative, zero, maximum, serialization, and date-boundary values.

The original issue also proposed clamping large positive durations. This change intentionally preserves every positive int32 duration because Kubernetes and client-go accept and honor those values. A unilateral cap could make a follower acquire before a legitimate holder's declared lease expires, creating two active leaders. Enforcing a smaller maximum would require a separately documented protocol constraint shared by all participants.

Checklist

• I have read and followed the CONTRIBUTING.md guidelines
• Passed make pre-commit (fmt-check + clippy + test + console-lint + console-fmt-check)
• Added/updated necessary tests
• Documentation updated (if needed)
• CHANGELOG.md updated under [Unreleased] (N/A: internal reliability fix with no user-facing workflow change)
• CI/CD passed (pending GitHub Actions)

Impact

• Breaking change (CRD/API compatibility)
• Requires doc/config/deployment update
• Other impact: invalid sub-second or out-of-range leader-election configurations now fail during construction instead of producing invalid Lease records.

Verification

make pre-commit

Additional Notes

Standard Kubernetes API validation rejects non-positive Lease durations, but the leader-election core also supports generic Lock implementations and must remain robust against malformed records. The Kubernetes adapter therefore preserves the wire value, while the core owns validity policy.

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