Improve transmission efficiency input data

[danielolsen]

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• Is your feature request essential for your project?

Describe the workflow you want to enable

Currently, each transmission line has a pre-defined efficiency value, based on its voltage see here. I wish these values were dependent on line length as well.

Describe your proposed implementation

Within the switchwrapper.grid_to_switch module, the build_aclines and build_dclines functions should be modified to look at the length of the line, and use this information with per-mile loss information stored in switchwrapper.const to calculate line-specific loss values.

Describe alternatives you've considered, if relevant

Alternatively, we could prompt the user for these values.