fix(security): scope introspection cache keys to the middleware instance

The introspection cache used the raw token as key in a shared cache.
Two instances with different providers or clients shared results. Keys
now use the same instance prefix as the verified-token cache.

token_manager.go

@@ -812,7 +812,7 @@ func (t *TraefikOidc) RevokeToken(token string) {
 	// from the introspection cache after revocation. Next request
 	// re-introspects and sees active=false.
 	if t.introspectionCache != nil {
-		t.introspectionCache.Delete(token)
+		t.introspectionCache.Delete(t.introspectionKey(token))
 	}
 
 	d := blacklistDuration(token)