Make it possible to create random public keys

This is useful for tests.

swap/src/bitcoin.rs

@@ -105,6 +105,13 @@ impl SecretKey {
 #[derive(Debug, Copy, Clone, Serialize, Deserialize, PartialEq)]
 pub struct PublicKey(Point);
 
+impl PublicKey {
+    #[cfg(test)]
+    pub fn random() -> Self {
+        Self(Point::random(&mut rand::thread_rng()))
+    }
+}
+
 impl From<PublicKey> for Point {
     fn from(from: PublicKey) -> Self {
         from.0