Enabled the use of clippy for the project.

[f0rki]

• Run clippy in CI
  • Require SAFETY documents in front of every unsafe block.
  • Set MSRV version in clippy.toml to avoid lints that break the MSRV
• Several fixes to make clippy happy
  • Ran cargo clippy --fix
  • Added some clippy exceptions
  • Added many SAFETY comments to unsafe blocks
• Tested MIRAI static analyzer to find "unintentional panics"
  • added some debug-build overflow checks to satsify MIRAI
  • Currently, installing MIRAI takes way too long in CI so it is disabled for now. Need to find a way to cache this (maybe a custom github action or docker container).