feat: `c` extension support

[clabby]

Overview

[!NOTE] WIP.

Adds support for the RVC extension, which is preferred by the most heavily supported RISC-V targets in rustc. More information can be found in the working document, which I'll update along the way of implementing support.

TODO

• [x] Assess supported c extension instructions for asterisc
  • Pretty much everything but FP ops. See the hackmd.
• [x] Decoding logic for various c extension instruction types.
• [x] Encoding logic for various base ISA instruction types.
• [x] Adjust program counter incrementation based on instruction size.
• [x] Instruction decompressor in fast package
  • [ ] Port to rvsol and slow
• [x] RISC-V standard c extension tests
• [x] Decompressor tests
• [x] Rust minimal example
  • [ ] New syscalls
    • [ ] Document Rust / glibc / llvm syscall usage for RISC-V linux targets.
  • [ ] symbol patches
• [ ] Final cleanup; Delete scripts, etc.