Avoid logger serialization behind shared EntityManager proxy

[jhoeller]

Since Apache Commons Logging itself does not provide serializability of Log instances (in contrast to an undocumented implementation characteristic of spring-jcl), we should avoid unnecessary logger serialization in common infrastructure instances. Otherwise, serialization attempts may fail against regular Commons Logging on the classpath (which is a supported scenario in Spring Framework 6.x as well, as an alternative to spring-jcl). That aside, this also improves the footprint in case of many @PersistenceContext EntityManager proxies in many repository classes.