Add serde feature

[d-sonuga]

For dusk-network/rusk/issues/2773 and #143.

To serialize AffineNielsPoint and ExtendedNielsPoint, I implemented dusk_bytes::Serializable for them.
But there is currently some uncertainty about the correctness of the approach used to serialize because I don't understand AffinePoint's serialization and I'm unsure about whether or not it will be relevant to AffineNielsPoint and ExtendedNielsPoint.
Edit: AffineNielsPoint and ExtendedNielsPoint have not being changed.

[Neotamandua]

LGTM from my side, but I'm waiting for a second approval from a maintainer of this repository

[Neotamandua]

Generally, looks good to me. But based on the other two PRs (dusk-network/bls12_381-bls#22 & dusk-network/jubjub-schnorr#30), and for consistency, I would suggest having the tests as integration tests rather than module tests. Also because the current module tests are testing the implementation for Fr, which is in another module.

Edit: After checking back, we can leave it as it is except for the tests for Fr. Can you move them into the respective Dusk.rs file of the Fr module?

[moCello]

Code looks good to me, but please also update the issue and pr description and add an entry to the changelog

[Neotamandua]

LGTM.

We can now aim for a 0.14.2 release of this crate tomorrow, so that we can proceed directly with the phoenix-core crate that depends on it.