[Studio] Validate metrics query windows

[Aias00]

Summary

• validate Prometheus range query windows before hitting the metrics source
• reject inverted or oversized time ranges and invalid step expressions
• cap generated samples to keep the Studio metrics proxy from issuing excessive Prometheus queries

Scope

• RocketMQ Studio contest scope: Track 1 / METRICS-01 Prometheus-backed observability
• Related to [studio][Feature] add Prometheus-backed observability #431

Tests

• JAVA_HOME=/Users/aias/Library/Java/JavaVirtualMachines/openjdk-21.0.2/Contents/Home mvn -Dtest=MetricsServiceTest,MetricsControllerTest,PrometheusMetricsSourceTest test
• JAVA_HOME=/Users/aias/Library/Java/JavaVirtualMachines/openjdk-21.0.2/Contents/Home mvn test
• git diff --check

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[Aias00]

Superseded by #637. Consolidated with related Metrics/Prometheus validation changes to reduce review overhead while preserving the same scoped fixes and tests.