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).

examples/acceptance_tests/110/aiken.lock

@@ -0,0 +1,7 @@
+# This file was generated by Aiken
+# You typically do not need to edit this file
+
+requirements = []
+packages = []
+
+[etags]

examples/acceptance_tests/110/aiken.toml

@@ -0,0 +1,9 @@
+name = "aiken-lang/acceptance_test_110"
+version = "0.0.0"
+license = "Apache-2.0"
+description = "Aiken contracts for project 'aiken-lang/110'"
+
+[repository]
+user = "aiken-lang"
+project = "110"
+platform = "github"

examples/acceptance_tests/110/lib/foo.ak

@@ -0,0 +1,39 @@
+type Foo {
+  Foo(Int, Never)
+  Bar
+}
+
+test never_is_none() {
+  let none: Option<Void> = None
+
+  trace @"Never": Never
+  trace @"None": none
+
+  let data_never: Data = Never
+  let data_none: Data = none
+
+  data_never == data_none
+}
+
+test never_pattern_match() {
+  when Foo(14, Never) is {
+    Foo(x, Never) -> x == 14
+    Bar -> False
+  }
+}
+
+test never_assignment() {
+  let Never = Never
+  True
+}
+
+test never_wrong_cast() fail {
+  let data: Data = Some(42)
+  expect _: Never = data
+}
+
+test never_ok_cast() {
+  let none: Option<Void> = None
+  let data: Data = none
+  expect _: Never = data
+}

examples/acceptance_tests/script_context/v3/aiken.lock

@@ -13,4 +13,4 @@ requirements = []
 source = "github"
 
 [etags]
-"aiken-lang/stdlib@v2" = [{ secs_since_epoch = 1724491200, nanos_since_epoch = 427525000 }, "cdbbce58b61deb385e7ea787a2e0fc2dc8fe94db9999e0e6275bc9c70e5796be"]
+"aiken-lang/stdlib@v2" = [{ secs_since_epoch = 1724760716, nanos_since_epoch = 700202000 }, "cdbbce58b61deb385e7ea787a2e0fc2dc8fe94db9999e0e6275bc9c70e5796be"]

examples/acceptance_tests/script_context/v3/validators/certificates.ak

@@ -71,7 +71,7 @@ validator purposes {
       Some(
         RegisterCredential {
           credential: VerificationKey(only0s),
-          deposit: Some(3_000_000),
+          deposit: None,
         },
       ) == list.at(certificates, 5)
 
@@ -79,7 +79,7 @@ validator purposes {
       Some(
         UnregisterCredential {
           credential: VerificationKey(only0s),
-          refund: Some(3_000_000),
+          refund: None,
         },
       ) == list.at(certificates, 6)