Decouple restrict_impl for threshold and scaling

[Giuseppe5]

Is your feature request related to a problem? Please describe.
Currently, we use the same restrict implementation for the scale coming from the stats/parameters/constant, and the threshold.
There might be cases where we want to decouple this.
E.g., in MX the threshold implementation assumes floor as rounding method during po2 computation, however there is no constraints on the restrict impl of the scale, and it can be decoupled.

Describe the solution you'd like
We could have two complete separate implementations with different keywords, as to avoid name clash during dependency injection.

Describe alternatives you've considered
Alternatively, following a similar structure of MSE, we could use SubInjector in dependencies to instantiate the same class twice, once for the threshold and once for the scale.

Additional context
More tests might be needed after this feature.
Dealing with dependencies and SubInjectors requires a bit of expertise.