Using checkpoint input_scale as the normalization scale saturates
FP4 values (all block scales = 448). The input_scale is a calibration
constant, NOT the amax/(6*448) normalization scale.
Reverted to dynamic amax/(6*448) for activation quantization.
The correct use of checkpoint input_scale is still under investigation.
Preserved: _w13_input_scale and _w2_input_scale in finalize_weights
for future use once we understand the correct alpha contract.