Perf: Replace BTree usage with VecMap

[kantai]

I spent some time replacing the BTreeMap usage in Clarity with a map implementation using a sorted vec. This could have some memory improvements and I’ve measured some limited runtime improvements while running block replay (5-10% maybe).

There’s probably plenty more gains to be had here: the fallible checked_from_vec function is faster than the From<Vec> implementation (which mimics the overwriting inserts behavior of a BTree) and there’s places where the checked_from_vec could be used instead of from(vec). There’s also likely even more opportunity to avoid reallocs by using with_capacity and reserve more aggressively (particularly in the merge functions?)

I started a branch with a prototype implementation of the data struct and its integration into Clarity tuples and type maps. There is some test coverage (this is a good candidate for property testing, btw) for the data structure as well:

https://github.com/stacks-network/stacks-core/blob/feat/vecmap/clarity/src/vm/types/vecmap.rs