verkle: rename verkle utils and refactor

[gabrocheleau]

This PR updates the verkle utils namespace so that they are clearer in the context of being exported from the util package rather than the verkle package. It also ports over some tests from verkle to util.

[holgerd77]

Cool, thanks for addressing so quickly, great to now have this "round"! 🙂 ❤️

I think I would be a fan of also moving matchingBytesLength() over to Util bytes, even if it might not be totally apparent if there will be other usages. But this is such a generic function that it's worth to "offer as a service" (who knows what other users are doing) and then we have this out of Verkle.

At along maybe we can even (already) move the PrioritizedTaskExecutor over and also integrate into Trie to make the round-trip. Would also make sense and then we can simply kill off the whole util folder from Verkle.