There are no changes visible from the user side (at least for those
users who doesn't put Prometheus's or pprof's port in quotes), just
internal refactoring. From now and on, BasicService configuration is
used by RPC server config, TLS for RPC server, pprof and Prometheus.
We have a lot of native contract types that are converted to stack items
before serialization, then deserialized as stack items and converted back to
regular structures. stackitem.Convertible allows to remove a lot of repetitive
io.Serializable code.
This also introduces to/from converter in testserdes which unfortunately
required to change util tests to avoid circular references.
