Creates a Callable gate set validator with a set message size.

This validator can be used for a validator in cg.ValidatingSampler and can also be useful in generating 'engine emulators' by using cg.SimulatedLocalProcessor with this callable as a validator.

max_moments Maximum number of moments to allow.
max_repetitions Maximum number of parameter sweep values allowed when summed across all sweeps and all batches.
max_duration_ns Maximum duration of the circuit, in nanoseconds.