Fix "copy constructor" in TestModeBuilder

The AZR instance was shared between the original ZenMode and the new one. Since it's not immutable, any further changes would affect both modes.

Bug: 361592187
Test: atest AutoDarkThemeTest
Flag: EXEMPT Fixing test utility
Change-Id: I03f4bbb8129da04f136d2ae791ba30d136bb13a7