lib/errors: switch to std Unwrap, Is, As

Created by: bobheadxi

Unify error assertions on standard library implementations, instead of cockroachdb implementations - the UnwrapOnce in that library supports Cause for back-compat, but Cause can have many meanings it seems

Discussion: https://sourcegraph.slack.com/archives/CHXHX7XAS/p1649709835518209

Test plan

TODO