perf: Improve the lattice reduction performance

[Yawning]

The lattice reduction implementation could likely be optimized further in the following ways:

• [ ] Add a 32-bit backend (Low priority, the current code provides adequate performance)
• [ ] Take a futher page out of curve9767's book and inline absolutely everything.
• [ ] Assembly?

As a datapoint, in a branch a partial implementation (panics on edge cases) of a fully inlined version of the lattice reduction was faster, but I'm not sure if the unreadable mess I ended up with is worth a ~2% improvement in signature verification performance.