v2.5.7 and v2.5.8.

Specifically, `AbstractHydrator#hydrateAll()` was raising
`E_NOTICE` errors due to it not being registered with the
`EventManager`, yet trying to remove itself from the
registered listeners. [#6623](https://github.com/doctrine/doctrine2/pull/6623)

In addition to that, having embeddable `final` classes
would cause errors being raised while trying to generate
proxies. The ORM will no longer attempt to generate proxies
for embeddables. [#6625](https://github.com/doctrine/doctrine2/pull/6623)

Total issues resolved: **3**

- [6623: Ensure that `AbstractHydrator#hydrateAll()` detaches the hydrator from the event manager](https://github.com/doctrine/doctrine2/pull/6623) thanks to @echo511
- [6625: Proxy generation for embedded/transient classes](https://github.com/doctrine/doctrine2/issues/6625) thanks to @bendavies
- [6626: #6625 Skip proxy generation for embeddable classes](https://github.com/doctrine/doctrine2/pull/6626) thanks to @issei-m