chore: add formatter section and re-enable null checks in equality operators

Author: orestesgaolin

codemagic_manager/analysis_options.yaml

@@ -68,4 +68,7 @@ linter:
     - avoid_positional_boolean_parameters # avoid
     - hash_and_equals
     - avoid_equals_and_hash_code_on_mutable_classes # avoid
-    - avoid_null_checks_in_equality_operators
+    - avoid_null_checks_in_equality_operators
+
+formatter:
+  page_width: 120