Reduce the features that the `ockam_macros` crate requires from `syn`

[thomcc]

In the ockam_macros crate, we require basically every feature of syn (by way of requiring full and extra-traits): https://github.com/ockam-network/ockam/blob/5a84ea59fd9d8a67b8e0585a6be312c6d54fc906/implementations/rust/ockam/ockam_macros/Cargo.toml#L32

This is probably more than we need, and slows down our build. It would be great if someone did some experimentation and figured out a more minimal feature-set for syn. I don't have a great suggestion for how to do this beyond trial and error, unfortunately.

[pro465]

sorry, but some of them require only "full" (like syn::Pat), and others "extra-traits" (like syn::Type: Debug). so unfortunately, they can't be removed.

[adrianbenavides]

We recently updated syn to version 2.0 and we still need the full feature.