Tokio runtime shutdown does not abort tasks created via `spawn_blocking`

[tankyleo]

In case these tasks never exit, this can cause Tokio runtime shutdown to hang indefinitely.

This is currently manifested here, which causes the 0FC Integration Tests to frequently time out:

ldk-node/src/lib.rs

Lines 339 to 346 in abbed3e

	self.runtime.block_on(async move {
	tokio::try_join!(
	chain_source.update_fee_rate_estimates(),
	chain_source.validate_zero_fee_commitments_support_if_required(
	zero_fee_commitments_support_required
	)
	)
	})?;

When concurrent requests share an Electrum client connection, a clean EOF can cause the active reader to return an error without waking other requests waiting on the connection. Those requests remain blocked in spawn_blocking, causing Tokio runtime shutdown to wait indefinitely for them to finish.