multiexp doesn't support caching tables between calls

[kayabaNerve]

I believe the optimal solution for this is instead of taking an G in, take in an Enum of G, SmallTable, or LargeTable (rough names, please don't use), allowing the caller to reuse where possible where multiexp expands the rest as needed.

Would notably speed up FROST key generation.

Related to #41, which is intending to provide large compile time tables.

[kayabaNerve]

Since we dynamically switch between Strauss/Pippenger (which have different tabling rules), this would be quite a pain. It's probably best not to do this in multiexp yet with a dedicated pippenger crate or within the context of its use case? Yet I can't say this will be actively worked on. PRs accepted.