Reverted the NO-FALLBACK rewrite of corex_gdn.py and qwen3_5.py.
Policy: do NOT rewrite modules that already exist in base image or
upstream_ref. If an interface doesn't match, fix the interface call
site — don't rewrite the entire module in pure PyTorch.
Base image has corex_gdn.py, corex_moe.py, corex_fa2.py with C++
backends. The right approach is to match their __init__ signatures,
not replace them with slower Python reimplementations.