fix: ensure tokio rt is always dropped on separate task

[mattsse]

previously we were dropping the tokio runtime on the current task, as described here:

reth/bin/reth/src/runner.rs

Lines 47 to 49 in ffe9691

	// drop the tokio runtime on a separate thread because drop blocks until its pools
	// (including blocking pool) are shutdown. In other words `drop(tokio_runtime)` would block
	// the current thread but we want to exit right away.

this causes issues with blocking tasks (pipeline), so in the panic case we did not always exit right away.

This ensures the tokio rt is always dropped on a separate task so we can exit right away.

[rkrasiuk]

🫡