Add test of never type in arrays (#6943)

## Description

Shows that #6387 has been fixed.

This PR adds a few tests of variable initializers that involve type
Never. In this case the variable's type ascription should be used
instead of the initializer's type.

No changes have been made to the compiler, since the problem that was
originally reported was fixed by #6911.


## Checklist

- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] If my change requires substantial documentation changes, I have
[requested support from the DevRel
team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [x] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

Author: jjcnn

test/src/e2e_vm_tests/test_programs/should_fail/unify_never/Forc.lock

@@ -0,0 +1,13 @@
+[[package]]
+name = "core"
+source = "path+from-root-DFCFC85C94C0C9BD"
+
+[[package]]
+name = "std"
+source = "path+from-root-DFCFC85C94C0C9BD"
+dependencies = ["core"]
+
+[[package]]
+name = "unify_never"
+source = "member"
+dependencies = ["std"]

test/src/e2e_vm_tests/test_programs/should_fail/unify_never/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+authors = ["Fuel Labs <contact@fuel.sh>"]
+license = "Apache-2.0"
+name = "unify_never"
+entry = "main.sw"
+
+[dependencies]
+std = { path = "../../../reduced_std_libs/sway-lib-std-assert" }

test/src/e2e_vm_tests/test_programs/should_fail/unify_never/src/main.sw

@@ -0,0 +1,22 @@
+script;
+
+// Test of unification of the Never type
+
+impl [u32;0] {
+    fn foo(self){
+        log("32");
+    }
+}
+
+impl [!;0] {
+    fn foo(self){
+        log("never");
+    }
+}
+
+fn main() {
+    let z:[u32;0] = [];
+
+    // Should fail because z gets the type of its type ascription
+    let y: [!;0] = z;
+}

test/src/e2e_vm_tests/test_programs/should_fail/unify_never/test.toml

@@ -0,0 +1,9 @@
+category = "fail"
+
+#check: $()error
+#check: $()Mismatched types
+#nextln: $()expected: [!; 0]
+#nextln: $()found:    [u32; 0].
+#nextln: $()help: Variable declaration's type annotation does not match up with the assigned expression's type
+
+#check: $()Aborting due to 1 error

test/src/e2e_vm_tests/test_programs/should_pass/language/unify_never/src/main.sw

@@ -13,7 +13,22 @@ fn test_2(){
 }
 
 
-fn main() {
+impl [u32;0] {
+    fn foo(self) -> u64 {
+        32
+    }
+}
+
+impl [!;0] {
+    fn foo(self) -> u64{
+        64
+    }
+}
+
+fn main() -> u64 {
     test_1();
     test_2();
+
+    let x:[u32;0] = [];
+    x.foo() // should return 32
 }

test/src/e2e_vm_tests/test_programs/should_pass/language/unify_never/test.toml

@@ -1,2 +1,5 @@
-category = "compile"
+category = "run"
 expected_warnings = 1
+expected_result = { action = "return", value = 32 }
+expected_result_new_encoding = { action = "return_data", value = "0000000000000020" }
+validate_abi = false