dx: Vet use of errors

Created by: efritz

Searched for uses matching the following patterns and rewrote them to use the cockroachdb/errors package in the most idiomatic way:

• errors.As(, use of As method
• errors.Is(, use of Is method
• errors.Cause( and .Cause(, use of unwrapping
• Searched for places where a custom causer interface was defined
• err.(, cast of error value