feat: Add From impls for TypeArg

hugr/src/types/type_param.rs

@@ -136,6 +136,30 @@ impl From<Type> for TypeArg {
     }
 }
 
+impl From<CustomTypeArg> for TypeArg {
+    fn from(arg: CustomTypeArg) -> Self {
+        Self::Opaque { arg }
+    }
+}
+
+impl From<TypeArgVariable> for TypeArg {
+    fn from(v: TypeArgVariable) -> Self {
+        Self::Variable { v }
+    }
+}
+
+impl From<ExtensionSet> for TypeArg {
+    fn from(es: ExtensionSet) -> Self {
+        Self::Extensions { es }
+    }
+}
+
+impl From<Vec<TypeArg>> for TypeArg {
+    fn from(elems: Vec<TypeArg>) -> Self {
+        Self::Sequence { elems }
+    }
+}
+
 /// A statically-known argument value to an operation.
 #[derive(Clone, Debug, PartialEq, Eq, serde::Deserialize, serde::Serialize)]
 #[non_exhaustive]