* update staticcheck
Don't fork staticcheck: use the upstream version.
Remove unneeded SSA loading.
* Cache go/analysis facts
Don't load unneeded packages for go/analysis.
Repeated run of go/analysis linters now 10x faster
(2s vs 20s on this repo) than before.
Significantly improve CPU and memory usage when not using SSA-powered linters.
Improve readability of go/packages errors.
Improve debugging capabilities and write doc about debugging.
