Change a bunch of code to use generics

[dnr]

What changed?

• Move common.Min/Max* and functions and a few others to new common/util package to prevent circular imports.
• Make Min/Max generic, except for Min/MaxTime, which need to use special time functions.
• Change a bunch of code to use slices.Clone, slices.Contains, maps.Clone, maps.Copy, maps.Keys, and maps.Values from golang.org/x/exp.
• Add generic common.CloneProto and switch users of proto.Clone
• service/matching/tasks.go can just use util.SortSlice
• Simplified surrounding code if it made sense.

I tried to keep this to only simple noncontroversial changes.

Why?
Clearer code

How did you test it?
Existing unit tests and integration tests

Potential risks
typos

Is hotfix candidate?
no

[dnr]

Some of the shard controller tests were flaky on my machine and it was hard to check the changes in there. I added a few sleeps to make them more reliable for now, but we should fix these with proper synchronization later. If you want I can merge without the sleeps