Add redpallas::signing_key::SigningKey stub

zebra-chain/src/primitives/redpallas/signing_key.rs

@@ -0,0 +1,19 @@
+use std::{
+    convert::{TryFrom, TryInto},
+    marker::PhantomData,
+};
+
+use halo2::pasta::pallas;
+
+use super::{SigType, VerificationKey};
+
+/// A RedPallas signing key.
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "serde", serde(try_from = "SerdeHelper"))]
+#[cfg_attr(feature = "serde", serde(into = "SerdeHelper"))]
+#[cfg_attr(feature = "serde", serde(bound = "T: SigType"))]
+pub struct SigningKey<T: SigType> {
+    sk: pallas::Scalar,
+    pk: VerificationKey<T>,
+}