feat(primitives): Add y_parity_byte_non_eip155 to Parity (#499)

* feat(primitives): add fn to get v as 27,28 in the case of a non eip155 sig

* rename

* Update crates/primitives/src/signature/parity.rs

Co-authored-by: Bjerg <onbjerg@users.noreply.github.com>

* feat: also apply + 27 in the simple Parity case

---------

Co-authored-by: Bjerg <onbjerg@users.noreply.github.com>

Author: Evalir

crates/primitives/src/signature/parity.rs

@@ -83,6 +83,15 @@ impl Parity {
         self.y_parity() as u8
     }
 
+    /// Return the y-parity byte as 27 or 28,
+    /// in the case of a non-EIP155 signature.
+    pub const fn y_parity_byte_non_eip155(&self) -> Option<u8> {
+        match self {
+            Self::NonEip155(v) | Self::Parity(v) => Some(*v as u8 + 27),
+            _ => None,
+        }
+    }
+
     /// Inverts the parity.
     pub const fn inverted(&self) -> Self {
         match *self {