Fix fare checking for basic fares

[razzamatazm]

fix fare checking for non-changeable basic fares by reading the booked WGA amount from the cancel refund quote API

• derive the current basic fare from change-shopping upgrade prices and price differences instead of treating WGA fares as unavailable
• add unit and integration coverage for WGA and WGARED fare checks

Testing

• .venv/bin/pytest -p no:rerunfailures tests/unit/test_fare_checker.py\n

• .venv/bin/pytest -p no:rerunfailures tests/integration/test_fare_checker.py

• Fixes Element {.login-button--box} was not present after 7 seconds! #379

• Fixes Basic Fares not being detected? #386

[razzamatazm]

Well - this works so long as the flyer doesn't have a companion linked to their reservation, as that requires cancelling the companion reservation first. I found a method of pulling the price paid in points if the flyer is using the account method of getting their reservations via the rapid rewards profile portal, but that does not provide purchase amounts in $$$. It's pretty obvious SW does not want to remind you how much you paid for your flights, as the price you paid for historical flights is very easily displayed.

[jdholtz]

Thanks @razzamatazm! Hoping to have the time to do a review of this in the next few days

[aaron-pham]

Would love to get this in! @jdholtz, sure you are busy though :P