Consider using noble-curves for keygen

[curves](https://github.com/paulmillr/noble-curves) recently got out. This could be an opportunity to:

1. Make API synchronous
2. Improve compatibility with environments where EC is not available in native webcrypto
3. Add support for additional curves, such as secp256k1, or any other curve, including custom ones.

As a side note, you're using hash-to-curve which is also implemented in curves.

We will probably publish an audit of the library some time soon.