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/not.json

@@ -407,16 +407,6 @@
                 "path": "",
                 "schema": "not_4_0"
               }
-            },
-            {
-              "code": "STRICT_ITEM_VIOLATION",
-              "values": {
-                "index": "0"
-              },
-              "details": {
-                "path": "0",
-                "schema": "not_4_0"
-              }
             }
           ]
         }
@@ -610,16 +600,6 @@
                 "path": "",
                 "schema": "not_5_0"
               }
-            },
-            {
-              "code": "STRICT_ITEM_VIOLATION",
-              "values": {
-                "index": "0"
-              },
-              "details": {
-                "path": "0",
-                "schema": "not_5_0"
-              }
             }
           ]
         }