fix: nested helmfile values should replace arrays, not merge element-by-element (#2458)

PR #2367 introduced CLIOverrides to give --state-values-set element-by-element
array merge semantics. However, nested helmfile values (helmfiles[].values:)
were also routed into CLIOverrides, causing their arrays to merge instead of
replace. This broke the pre-v1.3.0 behavior where passing an array via
helmfiles[].values: would fully replace the child's default array.

Add OverrideValuesAreCLI flag to SubhelmfileEnvironmentSpec so the loader can
distinguish CLI flags from nested helmfile values. CLI values continue using
CLIOverrides (element-by-element merge); nested helmfile values now use Values
(Sparse merge strategy → full array replacement).

Fixes #2451

Signed-off-by: Aditya Menon <amenon@canarytechnologies.com>

test/integration/test-cases/issue-2451-nested-helmfile-array-replace/input/child.yaml.gotmpl

@@ -0,0 +1,17 @@
+values:
+  - defaults.yaml
+
+---
+releases:
+  - name: test
+    chart: ../../../charts/raw
+    values:
+      - templates:
+          - |
+            {{- range $item := .Values.list }}
+            ---
+            apiVersion: v1
+            kind: ConfigMap
+            metadata:
+              name: {{ $item.name }}
+            {{- end }}

test/integration/test-cases/issue-2451-nested-helmfile-array-replace/input/defaults.yaml

@@ -0,0 +1,3 @@
+list:
+  - name: default1
+  - name: default2

test/integration/test-cases/issue-2451-nested-helmfile-array-replace/input/helmfile.yaml

@@ -0,0 +1,5 @@
+helmfiles:
+  - path: child.yaml.gotmpl
+    values:
+      - list:
+          - name: override1