Inputs need a `serialize_for_exchange` (or similar) method to serialize for sending them over the wire

Similar to how `to_file` works today (it serializes an input _for storage on disk_), we need a way to exchange inputs with other nodes.
Specifically, simply serializing inputs with Serde won't work for any input that references local fuzzer state, such as this: https://github.com/AFLplusplus/LibAFL/blob/4d3c6a3b9af1469dd253f2cc154822497b25b107/libafl/src/inputs/encoded.rs#L199

In this example, token mutations is builds up a mapping of tokens to ids internally, so deserializing with a different mapping will lead to useless inputs.
This means that sharing inputs right now may be broken for some input types.

In contrast to `to_file` we don't need to optimize storage size, for example, but speed of transfer / low amount of reruns.