Switch to Mint for CI/CD

[pierrebeaucamp]

Additionally:

• Fixes a pointer bug in some parsers that lead to incorrect results (was previously not caught by the linter)
• Removed Nix in favour of asdf
• Updates Go to 1.22 and runs the latest version of golangci-lint
• Restricts the backwards compatibility tests to run one version at a time, to ease pressure against our staging environment.

The last publish step in our CD pipeline is still untested. It also depends on https://github.com/rwx-research/infrastructure/pull/552 being merged beforehand.

Note also that this is missing an approval workflow (since that feature is still in development). Instead, the publish step will need to be launched manually using the Mint CLI for now.