Document convention of preferring named arguments even for mandatory (positional) args

Given the variety of backgrounds and experiences present across CFA and the fact that CFA members seem, at present time, to constitute most of MSRs early users, I suggest we explicitly write out the argument names for positional arguments.

Pro: The argument names provide useful information to new users of MSR, Python, and certain Python package (e.g., numpyro).

Con: Blurs the lines between required and optional arguments, as now all previously positional arguments are presented as keyword arguments.

Con: More writing for MSR developers.

Examples

I0 = InfectionInitializationProcess(
    "I0_initialization",
    DistributionalRV(dist=dist.LogNormal(2.5, 1), name="I0"),
    InitializeInfectionsZeroPad(pmf_array.size),
    t_unit=1,
)

...would change to

I0 = InfectionInitializationProcess(
    name="I0_initialization",
    I_pre_seed_rv=DistributionalRV(
        dist=dist.LogNormal(loc=2.5, scale=1), name="I0"),
    infection_seed_method=InitializeInfectionsZeroPad(
        n_timepoints=pmf_array.size),
    t_unit=1,
)

Further thoughts are welcome. I do not feel particularly strongly about this, I just believe it might help clarify things to people in the tutorials somewhat.