Fix some nits in bls12_381 precompiles

[jtraglia]

I was reviewing the new precompiles and noticed some stuff. This PR does the following:

• Fix a few typos.
• Replace g2 with g1 in extract_g1_input.
• Remove unnecessary type hint for input_fps.
• Rephrase comment about filtering points at infinity in the MSMs.
  • I found the part about returning bytes a little confusing.
  • We had to do the same thing in ckzg by the way 😢

These look great though. Didn't spot any real issues.

[Rjected]

thanks! I like the new comments, I think this just needs a fmt fix

[jtraglia]

thanks! I like the new comments, I think this just needs a fmt fix

Thanks! And oops, should be good now.

[rakita]

Thanks for review!
lgtm