Optimize memory instrinsics

[shaneutt]

Developers can run into problems with the BPF verifier like invalid size of register spill despite having what might not seem (to them) like a very large or complex eBPF program. The ways in which the developer of the eBPF program can deal with this are to reduce complexity in their own code, as well as things like moving some work into functions to ensure less registers need to be used at a single time. However @alessandrod has also recommended that we consider optimizing memory instrinsics (memset/memcpy/memmove, e.t.c.) as a way Aya itself can improve these situations.

The purpose of this task is to strategize and implement optimizations for our memory instrinsics in hopes of producing smaller code.

(originally discussed in #505, and recommended by @alessandrod)