📎 `derive(biome_deserialize::Deserializable)`: don't require the implementation of Default

[Conaclos]

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.