Improve performance

[conradoplg]

There are a bunch of low-ish hanging fruits to improve FROST performance:

• Use specific functions for fixed point multiplications
  - Use simultaneous point multiplications where possible (see how batch does it; requires Fix batching for curves with order larger than 256 bits (i.e. Ed448) #229) done: First stab at multiscalar speedup for computing group commitments #345
• Use more performant algorithms for multiscalar multiplication (Pippinger?)
• Use smaller blinding factor in batch verification and take advantage of it
• Use specific techniques for order checks in cofactored curves (see Pornin paper)

Not a priority but we might want to do them at some point.

[dconnolly]

Ha this may be resolved via #345