- bump versions
  - ubuntu -> 20.04
  - llvm -> 12 / 13
  - gcc -> 9 / 10
  - flint-dev -> latest github release
- fixes
  - disable cotire for asan
  - fix teuchos compiler warning about throwing from a destructor
    - copied with minor changes from https://github.com/trilinos/Trilinos/commit/9c3771bd6d74c724c281ae86b33f37bffa78db0b
- speedup
  - add ccache, with unique cache id for each job based on environment variables
  - use -j2 for make everywhere by default
- cleanup
  - remove unused environment variables
  - move coverage ci jobs back into main ci yml
  - remove binutils compilation
  - remove llvm apt install