Description

We currently require the implementation of Default for any type that implements Deserializable.
We should drop this requirement.

This implies that we should require the presence of any field that is not wrapped in an Option.
So, we could remove the required field attribute.

EDIT: I think it is not a good idea of requiring by default a field. biome_deserialize is used for deserializing config files where most of the fields are expected to be optional.
Thus, requiring a field by default seems not a good change because it could incur adding many annotations.
However, I still think we should drop the requirement of implementing Default.
Instead of calling Default::default() on the deserialized struct, we could call the Default::default() implementation of missing fields.
This moves the requirement of the struct to its optional fields.

Extra proposal

I am not sure if we need the next one. This could be left for the future.

We could add the support for the default struct attribute and the default field attribute to make a non-Option-wrapped field optional.