tests: move fixtures to dedicated dir

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I9d6ce6a264780f215b1b57d947b5264c6a6a6964

tests/fixtures/nested_attrs.nix

@@ -0,0 +1,13 @@
+# Test nested attribute paths
+{
+  # Simple nested path
+  a.b.c = 42;
+
+  # Multiple nested paths
+  x.y = 1;
+  x.z = 2;
+
+  # Mix of nested and non-nested
+  foo = "bar";
+  nested.deep.value = 100;
+}