chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/pprof/server_test.go

@@ -120,7 +120,7 @@ func Test_Server_BadSettings(t *testing.T) {
 
 	server, err := New(settings)
 	assert.Nil(t, server)
-	assert.ErrorIs(t, err, ErrBlockProfileRateNegative)
+	assert.ErrorContains(t, err, "block profile rate cannot be negative")
 	const expectedErrMessage = "pprof settings failed validation: block profile rate cannot be negative"
 	assert.EqualError(t, err, expectedErrMessage)
 }