KAFKA-20297: move Scheduler from client common to trogdor

[cychiu8]

Summary
This PR refactors the Scheduler utility and its implementations by moving them from the clients module to the
trogdor module. It also ensures that client-side tests that previously relied on MockScheduler remain
functional by implementing a local version where needed.

Key Changes

• Package Relocation: Moved Scheduler, SystemScheduler, and MockScheduler from org.apache.kafka.common.utils
  to org.apache.kafka.trogdor.common.
• Trogdor Updates: Updated all references in the trogdor module (including Agent, Coordinator, TaskManager,
  and WorkerManager) to point to the new location of the Scheduler interface and its implementations.
• Client Test Stability: Added a private MockScheduler inner class to
  ExpiringCredentialRefreshingLoginTest.java. This replaces the dependency on the global MockScheduler that
  was moved to Trogdor, keeping the clients module tests decoupled from trogdor.
• Cleaned Up Imports: Removed unused imports and updated package declarations across 13 files to reflect the
  architectural shift.