gofumpt

Enforce a stricter format than `gofmt`, while being backwards-compatible. That is, `gofumpt` is happy with a subset of the formats that `gofmt` is happy with. The tool is a fork of `gofmt` as of Go 1.19, and requires Go 1.18 or later. It can be used as a drop-in replacement to format your Go code, and running gofmt after gofumpt should produce no changes. `gofumpt` will never add rules which disagree with `gofmt` formatting. So we extend `gofmt` rather than compete with it.