fix: code gen tests now up to date using trace

fix: Formatter should take ErrorTerm and return "fail"
fix: fail with no reason should just return ErrorTerm

crates/aiken-lang/src/parser/expr/snapshots/fail_empty.snap

@@ -2,14 +2,6 @@
 source: crates/aiken-lang/src/parser/expr/fail_todo_trace.rs
 description: "Code:\n\nfail\n"
 ---
-Trace {
-    kind: Error,
+ErrorTerm {
     location: 0..4,
-    then: ErrorTerm {
-        location: 0..4,
-    },
-    text: String {
-        location: 0..4,
-        value: "aiken::error",
-    },
 }

crates/aiken-lang/src/parser/expr/when/snapshots/when_clause_solo_error.snap

@@ -24,16 +24,8 @@ When {
                 },
             ],
             guard: None,
-            then: Trace {
-                kind: Error,
+            then: ErrorTerm {
                 location: 28..32,
-                then: ErrorTerm {
-                    location: 28..32,
-                },
-                text: String {
-                    location: 28..32,
-                    value: "aiken::error",
-                },
             },
         },
     ],