Detect whether dynamic functions exist to save checking.

src/types/custom_types.rs

@@ -25,6 +25,11 @@ impl CustomTypesCollection {
     pub fn new() -> Self {
         Self(BTreeMap::new())
     }
+    /// Clear the [`CustomTypesCollection`].
+    #[inline(always)]
+    pub fn clear(&mut self) {
+        self.0.clear();
+    }
     /// Register a custom type.
     #[inline(always)]
     pub fn add(&mut self, type_name: impl Into<Identifier>, name: impl Into<Identifier>) {