Use a verifier instead of catch_unwind when deserializing network messages.

**Task description**

Use a flatbuffers verifier instead of relying on catch_unwind.

Previously this was not easily possible since verifiers were not exposed, but version 2.0 of the flatbuffers dependency does expose a verifier, which we should use.

The verifier should check that internal offsets are valid and do not lead to out-of-bounds errors or other problematic behaviour.