cluster model decoupling - declare the codegen (ember) version and implement iteration

src/BUILD.gn

@@ -55,6 +55,7 @@ if (chip_build_tests) {
   chip_test_group("tests") {
     deps = []
     tests = [
+      "${chip_root}/src/app/codegen-interaction-model/tests",
       "${chip_root}/src/app/interaction-model/tests",
       "${chip_root}/src/access/tests",
       "${chip_root}/src/crypto/tests",

src/app/ConcreteClusterPath.h

@@ -52,7 +52,7 @@ struct ConcreteClusterPath
     // to alignment requirements it's "free" in the sense of not needing more
     // memory to put it here.  But we don't initialize it, because that
     // increases codesize for the non-consumers.
-    bool mExpanded; // NOTE: in between larger members
+    bool mExpanded; // NOTE: in between larger members, NOT initialized (see above)
     ClusterId mClusterId = 0;
 };
 

src/app/codegen-interaction-model/BUILD.gn

@@ -0,0 +1,27 @@
+# Copyright (c) 2024 Project CHIP Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import("//build_overrides/chip.gni")
+# This source set is TIGHLY coupled with code-generated data models
+# as generally implemented by `src/app/util`
+#
+# Corresponding functions defined in attribute-storace.cpp/attribute-table.cpp must
+# be available at link time for this model to use
+#
+# Use `model.gni` to get access to:
+#   CodegenDataModel.cpp
+#   CodegenDataModel.h
+#
+# The above list of files exists to satisfy the "dependency linter"
+# since those files should technically be "visible to gn" even though we
+# are supposed to go through model.gni constants