Add serde traits for presignature public data and commitment

[alfonzii]

To be able to serialize presignatures as a whole also in CGGMP24, we need to derive serde traits for public data.

[survived]

Thanks for submitting it! Due to org policies, we can only merge PR if:

• commits are signed-off (there's a failing workflow with instructions how to fix it)
• commits are GPG signed

Could you sign-off commits and GPG-sign them?

Also, if you want this change to be released to crates-io after this PR is merged, could you update the lib version to 0.7.0-alpha.4?

[survived]

This alone is not sufficient, you also need to add this attribute, otherwise derived trait impl will be unusable

Suggested change

	#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
	pub struct PresignaturePublicData<E: Curve> {
	#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
	#[serde(bound = "")]
	pub struct PresignaturePublicData<E: Curve> {

[survived]

here as well