zcash_keys: Add `Address::to_transparent_address`

zcash_keys/CHANGELOG.md

@@ -10,6 +10,7 @@ and this library adheres to Rust's notion of
 - `no-std` compatibility (`alloc` is required). A default-enabled `std` feature
   flag has been added gating the `std::error::Error` usage.
 - `zcash_keys::keys::ReceiverRequirement`
+- `zcash_keys::Address::to_transparent_address`
 
 ### Changed
 - Migrated to `nonempty 0.11`

zcash_keys/src/address.rs

@@ -424,6 +424,18 @@ impl Address {
             },
         }
     }
+
+    /// Returns the transparent address corresponding to this address, if it is a transparent
+    /// address, a Unified address with a transparent receiver, or ZIP 320 (TEX) address.
+    pub fn to_transparent_address(&self) -> Option<TransparentAddress> {
+        match self {
+            #[cfg(feature = "sapling")]
+            Address::Sapling(_) => None,
+            Address::Transparent(addr) => Some(*addr),
+            Address::Unified(ua) => ua.transparent().copied(),
+            Address::Tex(addr_bytes) => Some(TransparentAddress::PublicKeyHash(*addr_bytes)),
+        }
+    }
 }
 
 #[cfg(all(