feat: parse change_table entries into interstate/intrastate

[danielolsen]

This branch adds a new script analyze/statelines.py to parse a change_table (with a grid) into lists of upgraded interstate and intrastate lines, with a corresponding test_statelines.py script. This testing functionality uses several testing tools added in the PR for carbon (#39): the tests/ folder in root, the context.py file to ensure that the tests always import the right version of PostREISE, and the mock objects in mocks.py.

[danielolsen]

The unit tests test the individual functions with the mocks. An integration test against the real object can be run as:

from powersimdata.scenario.scenario import Scenario
from postreise.analyze.statelines import classify_interstate_intrastate
scenario = Scenario('130')
classified = classify_interstate_intrastate(scenario)
print(classified)

[rouille]

Looks good