perf: revert back to hashmap

[chebbyChefNEQ]

revert back to hashmap for better performance for now.

[rok]

LGTM!

[wjones127]

I've removed nohash entirely, since we only use it for rowids. Because of the number of collisions it's not a good choice in general.

I briefly tested xxh3 against the default hash, and it turns out the default hash is still 2x faster. So we should stick with the default hash for now.

[westonpace]

If we end up changing it again let's make a type alias so it's easier in the future (but no need to do that today).