fix: pass required bus parameter to build_load_zones

[danielolsen]

Purpose

Fix a bug introduced in https://github.com/Breakthrough-Energy/SwitchWrapper/pull/20.

What is the code doing

Ensuring that we pass the required bus parameter to the build_load_zones function.

Testing

Tested manually using the newly-created mvp_empty_dataframe branch, which ensures that all placeholder functions return an empty data frame so that we are never stopped early by any to_csv calls on a NoneType object.

Before:

>>> from switchwrapper.grid_to_switch import grid_to_switch
>>> from powersimdata import Grid
>>> grid = Grid("Western")
Reading bus.csv
Reading plant.csv
Reading gencost.csv
Reading branch.csv
Reading dcline.csv
Reading sub.csv
Reading bus2sub.csv
Reading zone.csv
>>> grid_to_switch(grid, "output")
Please enter base study year (normally PowerSimData scenario year): 2030
Please enter the number of investment stages: 3
Multi stage expansion identified.
Please enter investment period year, separate by space: 2020 2025 2030
Please enter start year for each period, separate by space: 2020 2025 2030
Please enter end year for each period, separate by space: 2024 2029 2034
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\DanielOlsen\repos\bes\SwitchWrapper\switchwrapper\grid_to_switch.py", line 39, in grid_to_switch
    build_load_zones().to_csv(load_zones_filepath, index=False)
TypeError: build_load_zones() missing 1 required positional argument: 'bus'

After:

>>> from switchwrapper.grid_to_switch import grid_to_switch
>>> from powersimdata import Grid
>>> grid = Grid("Western")
Reading bus.csv
Reading plant.csv
Reading gencost.csv
Reading branch.csv
Reading dcline.csv
Reading sub.csv
Reading bus2sub.csv
Reading zone.csv
>>> grid_to_switch(grid, "output")
Please enter base study year (normally PowerSimData scenario year): 2030
Please enter the number of investment stages: 3
Multi stage expansion identified.
Please enter investment period year, separate by space: 2020 2025 2030
Please enter start year for each period, separate by space: 2020 2025 2030
Please enter end year for each period, separate by space: 2024 2029 2034
>>>

Time to review

2 minutes.