UNOMI-939/940: Scheduler dispatch and cache refresh race fixes

[sergehuber]

Plain-language summary

Apache Unomi runs background jobs on a schedule. Examples include cache refresh and maintenance tasks. It also keeps in-memory copies of configuration such as rules and segments.

Under load or during shutdown, several bugs were possible. The same job could run twice. A recurring job could not be stopped at some times. A scheduled cache reload could overwrite data that had just been saved.

This PR fixes these timing bugs. Operators and connected systems should see more stable behavior.

What changed

Scheduler

• Claim a task in one step before starting it. Only one thread can start the same task at a time.
• Allow cancel when a recurring task is briefly marked completed between runs. Before, cancel had no effect in that state.
• Improve shutdown handling. Recovery no longer overwrites the "interrupted by shutdown" state. A failed start no longer leaves a task blocked forever.

In-memory caches (rules, segments, definitions, etc.)

• Add a read/write lock per item type.
• A background refresh cannot run at the same time as a direct save or delete. This stops old data from replacing new data in the cache.

Tests

• Add a concurrency test for the cache lock.
• Increase timeouts on some unit tests that timed out on slow CI.

Test plan

• mvn -pl :unomi-services,:unomi-services-common,:unomi-tracing-impl -am test (targeted)
• CI integration tests

References

UNOMI-939, UNOMI-940, UNOMI-929