Add feature-gated serde support for Participant/ThresholdParams

These don't have secret data yet sometimes have value to be communicated.

crypto/dkg/src/lib.rs

@@ -38,6 +38,7 @@ pub mod tests;
 
 /// The ID of a participant, defined as a non-zero u16.
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Zeroize)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Participant(pub(crate) u16);
 impl Participant {
   pub fn new(i: u16) -> Option<Participant> {
@@ -123,6 +124,7 @@ pub(crate) fn validate_map<T, B: Clone + PartialEq + Eq + Debug>(
 /// Parameters for a multisig.
 // These fields should not be made public as they should be static
 #[derive(Clone, Copy, PartialEq, Eq, Debug, Zeroize)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct ThresholdParams {
   /// Participants needed to sign on behalf of the group.
   t: u16,