Add 'eval' command to evaluate target aiken function

Pretty useful for debbugging. Though, on second-thoughts, this is
  something we may want to review later and maybe have that done by
  default for tests.

  At the moment, we expects tests to unify to `bool`, and treat `false`
  values as failing tests. Yet, on failures, this gives little
  information about what's wrong with the test.

  It'd be nice to either have better way to assert in tests, or, to
  simply accept non-bool tests, and show whatever the test evaluates
  to as a debug output.

crates/lang/src/uplc.rs

@@ -96,7 +96,12 @@ impl<'a> CodeGenerator<'a> {
         }
     }
 
-    pub fn generate(&mut self, body: TypedExpr, arguments: Vec<TypedArg>) -> Program<Name> {
+    pub fn generate(
+        &mut self,
+        body: TypedExpr,
+        arguments: Vec<TypedArg>,
+        wrap_as_validator: bool,
+    ) -> Program<Name> {
         let mut ir_stack = vec![];
         let scope = vec![self.id_gen.next()];
 
@@ -113,7 +118,11 @@ impl<'a> CodeGenerator<'a> {
         }
 
         // Wrap the validator body if ifThenElse term unit error
-        term = builder::final_wrapper(term);
+        term = if wrap_as_validator {
+            builder::final_wrapper(term)
+        } else {
+            term
+        };
 
         for arg in arguments.iter().rev() {
             term = Term::Lambda {