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/session.go

@@ -13,7 +13,7 @@ import (
 type SessionEnder interface {
 	Decoder() httphelper.Decoder
 	Storage() Storage
-	IDTokenHintVerifier(context.Context) IDTokenHintVerifier
+	IDTokenHintVerifier(context.Context) *oidc.Verifier
 	DefaultLogoutRedirectURI() string
 }