fix: missing gate and generator for serialization (#369)

Add the missing gates and generator in the serializer that were added
with the PublicKeyOf operation.

Add a test for CircuitData serialization+deserialization to avoid these
kind of bugs in the future.

src/backends/plonky2/mainpod/mod.rs

@@ -578,7 +578,7 @@ pub(crate) fn rec_main_pod_circuit_data(
     )
 }
 
-fn cache_get_rec_main_pod_circuit_data(
+pub(crate) fn cache_get_rec_main_pod_circuit_data(
     params: &Params,
 ) -> CacheEntry<(
     RecursiveCircuitTarget<MainPodVerifyTarget>,