feat: Baseline FHE primitives (LWE, rLWE)

[0xJepsen]

We should prepare for an FHE boom and get some base FHE primitives down.

I watched this lecture a while back and thought it was pretty good.

LWE

[mrdaybird]

I was thinking of implementing this paper (https://eprint.iacr.org/2013/340.pdf). This scheme is conceptually simple to understand. I think it will be a good starting point.