Make SyncKeyGen NodeUid-aware.

This allows the caller to address nodes by ID instead of by index.

Also contains a few other minor changes that will be needed for
`DynamicHoneyBadger`.

mod.rs

@@ -104,7 +104,7 @@ impl Signature {
 }
 
 /// A secret key, or a secret key share.
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct SecretKey(Fr);
 
 impl Default for SecretKey {

poly.rs

@@ -390,8 +390,8 @@ impl BivarPoly {
     }
 }
 
-/// A commitment to a bivariate polynomial.
-#[derive(Debug, Clone, Serialize, Deserialize)]
+/// A commitment to a symmetric bivariate polynomial.
+#[derive(Debug, Clone, Serialize, Deserialize, Eq, PartialEq)]
 pub struct BivarCommitment {
     /// The polynomial's degree in each of the two variables.
     degree: usize,