### What this PR does / why we need it?
fix: support model-specific routed_scaling_factor in muls_add fusion
Previously, MulsAddFusionPass used a hardcoded scale=1.0, which failed
to match the x * routed_scaling_factor + y pattern in models like GLM5
that use routed_scaling_factor=2.5. This caused the muls_add fusion to
be skipped, leaving unoptimized mul+add operations.
This fix reads routed_scaling_factor from model config (defaulting to
1.0
for backward compatibility) and uses it as the pattern scale, enabling
correct fusion for GLM5 and other models with custom scaling factors.
Fixes: Unoptimized mul+add in GLM5 attention blocks
Tested: GLM5-W8A8 with routed_scaling_factor=2.5
### Does this PR introduce _any_ user-facing change?
### How was this patch tested?
- vLLM version: v0.16.0
- vLLM main:
15d76f74e2
Signed-off-by: liuchenbing <chenliumail@163.com>
Co-authored-by: liuchenbing <chenliumail@163.com>
640ecd1b77