refactor: sp1-lib, syscall docs

[jtguibas]

Overview

Refactor the sp1-lib crate in zkvm, and add testing for the ecdsa-core patch for k256 to the patch-testing program.

Details

• Simplify curve modules in sp1-lib. Create an AffinePoint trait which is re-used across curves.
  • Move ecrecover logic to ecdsa-core patch for maintainability ecdsa v0.16.9 sp1-patches/signatures#2. Note: Decision to refactor these crates was driven by the circular dependency caused when trying to patch k256.
  • Remove decompress_pubkey logic from BLS in sp1-lib.
• Add better documentation and use safer types for syscalls.

Note on SemVer

Includes backwards-incompatible changes in sp1-lib, but because it only causes issues for developers who are creating patches for crates themselves with sp1-lib (which is highly uncommon), we've decided to not update the major version of sp1-lib in this release, although that would follow convention.