Run lint and format checks in github actions

[markpash]

It would be nice to have a separate workflow that simply flags broken formatting and common mistakes with a linter.
It's enough to just run on linux-amd64.

Using gofumpt for formatting.
Using go vet for basic checks.
Using staticcheck to catch more mistakes.

p.s. run these tools locally on the main branch and you'll find plenty of things to fix :D