869 bug choices parameter for textfields on spell model have no effect

[augustjohnson]

Here's roughly what I did:

• Allowed spells to be nullable, due to empty data in spells-that-dont-suck.
• Added a validation method into import that that checks choice constraints on models, it should fail now on bad choices.
• Fixed a ton of spells with invalid casting_times, across srd-2024 and spells-that-dont-suck. I anticipate there remain some problems there, but the basics are within choices OR are null at this point, that's pretty good.
• Added some tests for the fields that were untested.