Strict typing the internal structs

This PR uses strict typing for all the internal SwapScript and
SwapTx structures.

This also removes two redundant dependency, rand and hex. These are already
available from the bitcoin library.

Cargo.toml

@@ -20,10 +20,8 @@ codegen-units = 1
 panic = "abort"
 
 [dependencies]
-hex = "0.4.3"
 serde = { version = "1.0.0", features = ["derive"] }
 serde_json = "1.0.0"
-rand_core = {version = "0.6.4", features = ["getrandom"]}
 ureq = {version = "2.8.0", features = ["json"]}
 bip39 = "2.0.0"
 electrum-client = "0.19.0"

src/error.rs

@@ -18,6 +18,7 @@ pub enum Error {
     BIP32(bitcoin::bip32::Error),
     BIP39(bip39::Error),
     Hash(bitcoin::hashes::FromSliceError),
+    Locktime(String),
 }
 
 impl From<electrum_client::Error> for Error {
@@ -139,3 +140,15 @@ impl From<bip39::Error> for Error {
         Self::BIP39(value)
     }
 }
+
+impl From<bitcoin::absolute::Error> for Error {
+    fn from(value: bitcoin::absolute::Error) -> Self {
+        Self::Locktime(value.to_string())
+    }
+}
+
+impl From<elements::locktime::Error> for Error {
+    fn from(value: elements::locktime::Error) -> Self {
+        Self::Locktime(value.to_string())
+    }
+}