Cleaner txpool shutdown

[carver]

What was wrong?

The transaction pool was hanging on shutdown, because it had a bare await that doesn't get cancelled when the service is cancelled.

This shows up in an INFO log as:

Timed out waiting for <...TxPool...> to finish its cleanup, forcibly cancelling pending tasks and exiting anyway

How was it fixed?

Added a couple self.wait()s. Now that log doesn't show up anymore, and the shutdown is a bit faster.

Bonus changes:

• Linter fix, as in Mysterious spontaneous linter issues #1357
• Add a warning when beam sync skips ahead. This warning doesn't show up when beam sync is continued from the last synced block.

To-Do

• Clean up commit history

• Add entry to the release notes

Cute Animal Picture

[carver]

Is there any chance #1362 is related to this PR? It seems unlikely, but wanted to get more 👀 on it from @cburgdorf before merging.

[carver]

#1362 Seems very unlikely to be related to this, since #1354 has the same error in CI.

So I'll go ahead and rage-merge this.