Use unsafe_cleanup!/1 to delete data after consumer has stopped

[magnetised]

When cleaning up a shape we call cleanup! and (in the case of FileStorage) attempt to remove the data directory while the CubDb process is still running.

This fails (File.rm_rf/1 returns {:error, :eexist, _}) because the files are still in use.

Instead of removing the directory on cleanup! while the process(es) are still running, instead teardown the consumer supervision tree and use unsafe_cleanup!/1 do remove the directories.

unsafe_cleanup! is already documented as something that should be runnable without any active processes, so this is an ideal use.

Fixes problems with https://github.com/electric-sql/stratovolt/pull/243

[msfstef]

Nice! Fixes a sentry error I wanted to chase up on as well, two birds with one stone - more unsafe cleanups is the way!