Enable [`forcetypeassert`](https://github.com/gostaticanalysis/forcetypeassert)
linter to prevent unchecked type assertions. ~650 issues fixed, most
fixes were clean, some use `setting.PanicInDevOrTesting`.
The only behaviour changes are where code would previously send a 500 error
or panic, a 4xx error is now emitted.
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Introduce RequestContext: is a short-lived context that is used to store
request-specific data.
RequestContext could be used to clean form tmp files, close context git
repo, and do some tracing in the future.
Then a lot of legacy code could be removed or improved. For example:
most `ctx.Repo.GitRepo.Close()` could be removed because the git repo
could be closed when the request is done.
