Introduce 'Never' type as a safe alternative to always None options

Unfortunately, as documented in:

  https://github.com/IntersectMBO/cardano-ledger/issues/4571

  Some Option fields in the script context certificates are going to
  remain set to None, at least until the next Hard fork. There's a risk
  that people permanently lock their funds if they expect deposits on
  registration credentials to ever be `Some`.

  So, we introduce a special type that emulate an `Option` that can only
  ever be `None`. We call it `Never` and it is the first type of this
  kind (i.e. with constructors indexes not starting at 0).

crates/aiken-lang/src/ast/well_known.rs

@@ -16,6 +16,8 @@ pub const LIST: &str = "List";
 pub const MILLER_LOOP_RESULT: &str = "MillerLoopResult";
 pub const OPTION: &str = "Option";
 pub const OPTION_CONSTRUCTORS: &[&str] = &["Some", "None"];
+pub const NEVER: &str = "Never";
+pub const NEVER_CONSTRUCTORS: &[&str] = &["__hole", "Never"];
 pub const ORDERING: &str = "Ordering";
 pub const ORDERING_CONSTRUCTORS: &[&str] = &["Less", "Equal", "Greater"];
 pub const PAIR: &str = "Pair";
@@ -297,6 +299,17 @@ impl Type {
         })
     }
 
+    pub fn never() -> Rc<Type> {
+        Rc::new(Type::App {
+            public: true,
+            contains_opaque: false,
+            name: NEVER.to_string(),
+            module: "".to_string(),
+            args: vec![],
+            alias: None,
+        })
+    }
+
     pub fn ordering() -> Rc<Type> {
         Rc::new(Type::App {
             public: true,