[Fix] Initialize procedure worker list eagerly

[Caideyipi]

Description

Follow-up to #18338.

• Initialize workerThreads once as a final CopyOnWriteArrayList instead of publishing a mutable collection through a volatile reference.
• Clear and repopulate the list during initialization.
• Keep procedure metrics safe before and during ConfigNode leader initialization.

Tests

• mvn -pl iotdb-core/confignode -Dtest=TestProcedureExecutor -Ddevelocity.off=true test (9 tests)
• Checkstyle and Spotless checks included in the Maven run
• git diff --check