test: Add preserveAlertState, checkPMGQuarantineBacklog, LoadActiveAlerts tests
Add comprehensive tests for three low-coverage functions:
- preserveAlertState: nil handling, state preservation from existing alerts,
ackState fallback, new alert handling
- checkPMGQuarantineBacklog: nil quarantine handling, warning/critical
thresholds, growth rate alerts, alert updates, virus quarantine
- LoadActiveAlerts: missing file, valid file loading, old alert filtering,
old acknowledged alert filtering, ack state restoration, invalid JSON,
duplicate alert handling
Coverage improvements:
- preserveAlertState: 63.6% → 100%
- checkPMGQuarantineBacklog: 12.9% → 100%
- checkQuarantineMetric: 0% → 93.1%
- LoadActiveAlerts: 26.2% → 80.0%
- Alerts package: 83.5% → 86.6%
a4e3fe65b8