feat(bigquery-jdbc): migrate statement execution thread tracking to connection-scoped executor

[Neenu1995]

No description provided.

[gemini-code-assist]

Code Review

This pull request refactors background task management across several result set and statement classes to use Future instead of raw Thread references, mitigating potential out-of-memory errors by introducing a bounded cached thread pool. A temporary compatibility bridge wrapThread is added to BigQueryDatabaseMetaData to wrap raw threads into Futures. Feedback on the changes points out a missing import for CancellationException in BigQueryDatabaseMetaData.java which would cause a compilation error.

[gemini-code-assist]

The class CancellationException is used in the wrapThread method but is not imported in this file. This will cause a compilation error. Please add the import for java.util.concurrent.CancellationException.

Suggested change

	import java.util.concurrent.Future;
	import java.util.concurrent.LinkedBlockingQueue;
	import java.util.concurrent.TimeUnit;
	import java.util.concurrent.TimeoutException;
	import java.util.concurrent.CancellationException;
	import java.util.concurrent.Future;
	import java.util.concurrent.LinkedBlockingQueue;
	import java.util.concurrent.TimeUnit;
	import java.util.concurrent.TimeoutException;