Enable customizing runtime used for spawning blocking tasks inside the SyncConnectionWrapper #393

Job	Run time
Check rustfmt style && run clippy	1m 8s
Check Minimal supported rust version (1.78.0)	43s
Check (stable, postgres, ubuntu-latest)	2m 8s
Check (stable, postgres, macos-13)	3m 25s
Check (stable, mysql, ubuntu-latest)	3m 24s
Check (stable, mysql, macos-13)	7m 26s
Check (stable, mysql, ubuntu-22.04-arm)	3m 44s
Check (stable, postgres, macos-15)	2m 5s
Check (stable, sqlite, ubuntu-latest)	58s
Check (beta, mysql, ubuntu-latest)	3m 28s
Check (stable, mysql, macos-15)	2m 12s
Check (stable, postgres, ubuntu-22.04-arm)	2m 49s
Check (stable, sqlite, macos-15)	43s
Check (nightly, postgres, ubuntu-latest)	2m 9s
Check (stable, sqlite, windows-latest)	3m 10s
Check (stable, mysql, windows-latest)	8m 27s
Check (stable, sqlite, ubuntu-22.04-arm)	1m 18s
Check (beta, sqlite, ubuntu-latest)	2m 9s
Check (beta, postgres, ubuntu-latest)	2m 7s
Check (nightly, sqlite, ubuntu-latest)	55s
Check (nightly, mysql, ubuntu-latest)	3m 15s
Check (stable, postgres, windows-latest)	7m 52s
Check (stable, sqlite, macos-13)	1m 12s
	1h 6m 47s

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