Enable getting the network kind from an address

Users may wish to ask of an address 'what kind of address is this?' We
have the `NetworkKind` struct that abstracts over the answer but
currently no API to ask the question.

The address may have been parsed or constructed and weather the network
has been checked already is immaterial. Hence we add the function for
both `NetworkChecked` and `NetworkUnchecked` addresses.

Fix: #4247

bitcoin/src/address/mod.rs

@@ -273,6 +273,16 @@ impl From<Network> for KnownHrp {
     fn from(n: Network) -> Self { Self::from_network(n) }
 }
 
+impl From<KnownHrp> for NetworkKind {
+    fn from(hrp: KnownHrp) -> Self {
+        match hrp {
+            KnownHrp::Mainnet => NetworkKind::Main,
+            KnownHrp::Testnets => NetworkKind::Test,
+            KnownHrp::Regtest => NetworkKind::Test,
+        }
+    }
+}
+
 /// The data encoded by an `Address`.
 ///
 /// This is the data used to encumber an output that pays to this address i.e., it is the address
@@ -450,6 +460,16 @@ impl<V: NetworkValidation> Address<V> {
 
     /// Marks the network of this address as unchecked.
     pub fn into_unchecked(self) -> Address<NetworkUnchecked> { Address(self.0, PhantomData) }
+
+    /// Returns the [`NetworkKind`] of this address.
+    pub fn network_kind(&self) -> NetworkKind {
+        use AddressInner::*;
+        match self.0 {
+            P2pkh { hash: _, ref network } => *network,
+            P2sh { hash: _, ref network } => *network,
+            Segwit { program: _, ref hrp } => NetworkKind::from(*hrp),
+        }
+    }
 }
 
 /// Methods and functions that can be called only on `Address<NetworkChecked>`.