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/properties.json

@@ -489,16 +489,6 @@
                 "path": "constructor",
                 "schema": "properties_4_0"
               }
-            },
-            {
-              "code": "STRICT_PROPERTY_VIOLATION",
-              "values": {
-                "property_name": "length"
-              },
-              "details": {
-                "path": "constructor/length",
-                "schema": "properties_4_0"
-              }
             }
           ]
         }