test: clean up backup and transaction resources

[warku123]

Summary

• Close backup server, channels, and executors deterministically in backup tests.
• Replace timing-dependent smart-contract scheduler coverage with a production-typed queue and latch-based completion observation.
• Close handler and preserved executor resources after reflective test replacement.

Validation

• ./gradlew :framework:checkstyleTest --no-daemon --no-build-cache --console=plain
• Focused/ordered local regression runs completed before submission.
• Fork JDK 8 CI validation: 3 rerun attempts × 3 fresh matrix rounds; 17 targeted tests per round, retry disabled, single worker/shared JVM, all test and JaCoCo report exits zero.
  https://github.com/warku123/java-tron/actions/runs/29813505519

The temporary verifier workflow/property are intentionally not part of this PR.