`get_current_rule` is incorrectly a noop

## Expected Behavior
It should be an op, or at least a [`raise NotImplementedError`](https://docs.python.org/3/library/exceptions.html#NotImplementedError)

## Actual Behavior
#75 by @liudangyi created this [noop](https://en.wikipedia.org/wiki/NOP_(code)) 5-days ago in 354ceb9:
```py
def get_current_rule(op_name: str) -> QuantizationRule | None:
"""Returns the current quantization rule if intercepted, or None otherwise."""
del op_name
return None
```
https://github.com/google/qwix/blob/8f1a822/qwix/_src/qconfig.py#L92-L95

FWIW: `process_model_output` seems to be a similar function that is a noop stub.

## Steps to Reproduce the Problem

## Specifications

- Version: still true at latest `main` (354ceb9)