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/database.json

@@ -151,9 +151,9 @@
             {
               "code": "EDGE_MISSING",
               "values": {
-                "child_type": "child",
                 "property_name": "children",
-                "parent_type": "parent"
+                "parent_type": "parent",
+                "child_type": "child"
               },
               "details": {
                 "path": "full.parent/children",
@@ -390,9 +390,9 @@
             {
               "code": "AMBIGUOUS_TYPE_RELATIONS",
               "values": {
-                "parent_type": "actor",
+                "property_name": "ambiguous_edge",
                 "child_type": "junction",
-                "property_name": "ambiguous_edge"
+                "parent_type": "actor"
               },
               "details": {
                 "path": "full.actor/ambiguous_edge",