Adds a `make check` target that verifies formatting (gofmt), linting (golangci-lint), and tests (go test -race) without modifying files.
Also adds `.gitea/workflows/check.yml` CI workflow that runs on pushes and PRs to main and next.
`make check` passes cleanly on current next branch.
Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Reviewed-on: #36
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
