Generate metric scheduling intervals lazily

[zqr10159]

Summary

• generate exact metric refresh delays lazily instead of precomputing a full least-common-multiple cycle
• preserve explicit one-time timer overrides and a positive fallback interval
• make the standalone least-common-multiple helper fail fast on overflow

Validation

• ./mvnw -pl hertzbeat-common-core -Dtest=JobTest test -DskipITs -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false
• ./mvnw -pl hertzbeat-collector/hertzbeat-collector-common -am -Dtest=JobTest,TimerDispatcherTest test -DskipITs -Dsurefire.failIfNoSpecifiedTests=false -DfailIfNoTests=false
• git diff --check

AI assistance: used for draft implementation and test iteration.
Human validation: focused common-core and timer-dispatcher tests passed (15 tests total), with Checkstyle and diff hygiene passing.
Risk notes: collector-local scheduling state is now generated on demand; serialized job fields and explicit timer overrides remain unchanged.