feat: Implement serde::Serialize and serde::Deserialize for integers and floats

[xdoardo]

As per title: an initial contribution towards a broader implementation of serde's traits. As of now, the implementations are feature gated.

Let me know if the general structure is good enough, and then we can figure out what's the best way to test the implementations.

[djkoloski]

We should probably be calling serde's separate serialize_* methods on Serializer to retain the underlying types in the data model. For example, serializing a u64_le should call serialize_u64 so the backend can decide how best to represent it.

[djkoloski]

Clarifying: serde doesn't have a notion of endianness in its data model, so these should serialize as regular integers and floats.