Update error locations

Instead of flagging the entire declaration as erroneous, we only
indicate the problematic expression now.

Author: Shon Feder

quint/io-cli-tests.md

@@ -142,7 +142,7 @@ quint typecheck ./testFixture/TrivialTypeError.qnt 2> >(sed "s:$(pwd):.:" >&2)
 Trying to unify str and int
 
 2:   val x : int = "not an int"
-     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+                   ^^^^^^^^^^^^
 
 error: typechecking failed
 ```
@@ -1036,7 +1036,7 @@ HOME/testFixture/typechecking/FileWithError.qnt:2:3 - error: [QNT000] Couldn't u
 Trying to unify bool and int
 
 2:   val a: int = true
-     ^^^^^^^^^^^^^^^^^
+                  ^^^^
 
 error: typechecking failed
 ```