[wrapq] Bug in _all_observers()

[CMDR-DiTRay]

What?

The _all_observers() method in Quantization Wrappers yields observers from child modules, but the child modules (PTQWrapper instances) don't actually own observers themselves.

When the _all_observers() method in the parent modules (like QuantQwen3VLTextMLP, QuantQwen3VLTextAttention, etc.) calls yield from m._all_observers() on a PTQWrapper instance, it gets an empty iterator because:

1. PTQWrapper._all_observers() returns an empty iterator ()
2. The actual observers are owned by the wrapped module inside the PTQWrapper

Where?

This affetcs at least TextAttention (tico/quantization/wrapq/wrappers/qwen_vl/quant_text_attn.py) and Qwen3VLVisionMLP (tico/quantization/wrapq/wrappers/qwen_vl/quant_vision_mlp.py) Quantization Wrappers.