BedDays availability switch now correctly updates capacities

[willGraham01]

Fixes #1346

• A new method, switch_beddays_availability has been created to handle all steps necessary when switching the availability of beds.
• An appropriate test for this method has been added. There is scope to parametrise this test to check other possible inputs for availability, but this in itself should be covered if we are already testing the set_scaled_capacity method which the new method depends on.

[tbhallett]

Thanks @willGraham01

[tbhallett]

The way in which we expect to use this (i.e., from HealthSystemChangeParameters) I think we can always assume that this is equal to today's date. This is the way in which other things (consumables, equipment) have their availability updated.

[matt-graham]

With regards to this and the below comment - I think exposing effective_on_and_from and model_to_data_popsize_ratio as arguments has an advantage in terms of making it easier to test (as we can pass in relevant values directly rather than having to manipulate the other objects they would be instead read from) and keeping it's implementation decoupled from implementation details of other classes, however we can possibly still achieve this by making the current switch_beddays_availability method instead _switch_beddays_availability to indicate for internal use only, and exposing a 'public' method

   def switch_beddays_availability(self, new_availability: Literal["all", "none", "default"]) -> None:
        """..."""
        self._switch_beddays_availability(
            new_availability=new_availability, 
            effective_on_and_from=self.sim.date,
            model_to_data_popsize_ratio=self.sim.modules["Demography"].initial_model_to_data_popsize_ratio
        )

This would still allow using the current _switch_beddays_availability implementation in tests.

[willGraham01]

Happy to make a public/private method like is suggested above, though I'd quite like to avoid spreading the self.sim.modules... cross-class-coupling into the bed-days class if possible. switch_beddays_availability is already called by classes that have this cross-class-coupling anyway, so it might as well stay isolated to there?

[tbhallett]

it would be nicer (I think) if the user didn't need to pass this. It hasn't changed since the beginning of the simulation, so it seems awkward to pass it in just to instruct a change in availability to all/none/default.

[matt-graham]

I'm not super familiar with bed days system but this generally looks sensible from what I can tell. Added a couple of minor comments.

[matt-graham]

With regards to this and the below comment - I think exposing effective_on_and_from and model_to_data_popsize_ratio as arguments has an advantage in terms of making it easier to test (as we can pass in relevant values directly rather than having to manipulate the other objects they would be instead read from) and keeping it's implementation decoupled from implementation details of other classes, however we can possibly still achieve this by making the current switch_beddays_availability method instead _switch_beddays_availability to indicate for internal use only, and exposing a 'public' method

   def switch_beddays_availability(self, new_availability: Literal["all", "none", "default"]) -> None:
        """..."""
        self._switch_beddays_availability(
            new_availability=new_availability, 
            effective_on_and_from=self.sim.date,
            model_to_data_popsize_ratio=self.sim.modules["Demography"].initial_model_to_data_popsize_ratio
        )

This would still allow using the current _switch_beddays_availability implementation in tests.