fix: address adversarial review findings on metrics/telemetry archite…

[fupelaqu]

…cture (#17)

• Add ClusterApi.clusterUuid across all ES versions (6/7/8/9) so telemetry uses the real ES cluster UUID instead of the cluster name as identifier
• Make TelemetryCollector thread-safe with synchronized lock for gauge fields and add collectAndReset for atomic snapshot+reset
• Make MetricsCollector.resetMetrics atomic via AtomicReference map swap, add collectAndResetAggregatedMetrics to MetricsApi trait
• Replace synchronized+set() with pure CAS and @tailrec in LicenseRefreshStrategyFactory, remove try/catch fallback (let SPI failures propagate)
• Add ClusterApiSpec integration tests for clusterName and clusterUuid
• Add TelemetryCollectorSpec test for collectAndReset