refactor: run gofmt across all files

[G-Rath]

This is the result of manually running gofmt -s -w . in preparation for setting up golangci-lint to actually enforce this

Relates to #158

[G-Rath]

I have cherry-picked this into #264 as well, which enables the linter but requires #262 to be landed first - I don't mind which PR gets landed

[erikvarga]

Note that we'd have to enable some similar linter internally otherwise any code submitted from there might still have formatting that goes against gofmt formatting (specifically the internal auto-formatter doesn't seem to do the superfluous struct type removal)

[G-Rath]

specifically the internal auto-formatter doesn't seem to do the superfluous struct type removal

My understanding is that's a result of the -s, which tries to simplify code - I wouldn't be surprised if you've already got a gofmt linter and just need to start passing -s to it?