test(jspg): rename items fixture to array and resolve unused HashMap warning

- Rename fixtures/items.json to fixtures/array.json to better reflect array testing constraints.
- Update reference paths in src/tests/fixtures.rs and across other fixture JSON files.
- Remove unused HashMap import in src/validator/rules/dict.rs to resolve the compiler warning.

fixtures/merge.json

@@ -239,8 +239,8 @@
             {
               "code": "DEPENDENCY_MISSING",
               "values": {
-                "property_name": "trigger",
-                "required_property": "base_dep"
+                "required_property": "base_dep",
+                "property_name": "trigger"
               },
               "details": {
                 "path": "",