fix(evaluator-refs): inline is_ballmer logic in is_privileged, remove nested $ref

Addresses toddbaert's review concern: nested $ref resolution relies on
JSON key declaration order, which is non-deterministic when serialised by
a server (see open-feature/flagd#1875). Inlining the is_ballmer condition
directly into is_privileged eliminates the dependency and ensures
deterministic behaviour across all conformance implementations.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Simon Schrottner <simon.schrottner@dynatrace.com>

Author: aepfli

evaluator/flags/testkit-flags.json

@@ -497,7 +497,7 @@
     },
     "is_privileged": {
       "or": [
-        {"$ref": "is_ballmer"},
+        {"==": ["ballmer@macrosoft.com", {"var": ["email"]}]},
         {"==": ["admin", {"var": ["role"]}]}
       ]
     }

flags/evaluator-refs.json

@@ -66,7 +66,12 @@
     },
     "is_privileged": {
       "or": [
-        {"$ref": "is_ballmer"},
+        {
+          "==": [
+            "ballmer@macrosoft.com",
+            {"var": ["email"]}
+          ]
+        },
         {
           "==": [
             "admin",