feat: merge the verifier types

BREAKING CHANGE:

- The various verifier types are merged into a oidc.Verifir.
- oidc.Verfier became a struct with exported fields

pkg/op/auth_request_test.go

@@ -146,7 +146,7 @@ func TestValidateAuthRequest(t *testing.T) {
 	type args struct {
 		authRequest *oidc.AuthRequest
 		storage     op.Storage
-		verifier    op.IDTokenHintVerifier
+		verifier    *oidc.Verifier
 	}
 	tests := []struct {
 		name    string