In block processing, depending on the complexity of a transaction and
hotness of caches etc, signature checking can actually make up the
majority of time needed to process a transaction (60% observed in some
randomly sampled block ranges).
Fortunately, this is a task that trivially can be offloaded to a task
pool similar to how nimbus-eth2 does it.
This PR introduces taskpools in the most simple way possible, by
performing signature checking concurrently with other TX processing,
assigning a taskpool task per TX effectively.
With this little trick, we're in gigagas land 🎉 on my laptop!
```
INF 2024-12-10 21:05:35.170+01:00 Imported blocks
blockNumber=3874817 b... mgps=1222.707 ...
```
Tests don't use the taskpool for now because it needs manual cleanup and
we don't have a good mechanism in place. Future PR:s should address this
by creating a common shutdown sequence that also closes and cleans up
other resources like the DB.
f68a5d419f