Handle deserialization exceptions thrown from the deserialiser

Workaround: use byte[],byte[] for key value types, use Serdes' to deserialise yourself in the processing function, throw a terminal failure if you want to skip the message.

see:
- #291

Start by reading the linked issue #291 and tracing the deserialization and processing entry points it identifies. The issue does not name a file or test; done should mean deserialization exceptions are handled by the library rather than requiring callers to use byte arrays and deserialize manually.

Written by the indexing model from the issue text.