Clear notetypes cache on import

[abdnh]

Noticed this is needed after importing a deck with merge_notetypes enabled (which added a new template to a notetype) then opening the Card Types screen and getting this error:

Traceback (most recent call last):
  File "D:\dev\anki\repo\qt\aqt\webview.py", line 747, in handler
    cb(val)
  File "D:\dev\anki\repo\qt\aqt\editor.py", line 649, in <lambda>
    self.web.evalWithCallback("saveNow(%d)" % keepFocus, lambda res: callback())
  File "D:\dev\anki\repo\qt\aqt\editor.py", line 380, in _onCardLayout
    CardLayout(
  File "D:\dev\anki\repo\qt\aqt\clayout.py", line 92, in __init__
    self.redraw_everything()
  File "D:\dev\anki\repo\qt\aqt\clayout.py", line 106, in redraw_everything
    self.update_current_ordinal_and_redraw(self.ord)
  File "D:\dev\anki\repo\qt\aqt\clayout.py", line 113, in update_current_ordinal_and_redraw
    self.fill_fields_from_template()
  File "D:\dev\anki\repo\qt\aqt\clayout.py", line 488, in fill_fields_from_template
    t = self.current_template()
  File "D:\dev\anki\repo\qt\aqt\clayout.py", line 485, in current_template
    return self.templates[self.ord]
IndexError: list index out of range

I guess any backend operation on note types should invalidate the cache. We can add this to AnkiQt.on_operation_did_execute() but then the cache will be less useful when there are any updates:

if changes.notetype:
    self.col.models._clear_cache()

[dae]

I think your other proposal might be a better option Abdo. Explicitly clearly the cache on import doesn't solve the inverse problem, where the user undoes the import again, and there may be other situations where we should be invalidating the cache but are not. I'm not so worried about a less-useful cache - unless the notetype is being rapidly updated, the occasional extra cache miss is unlikely to be perceptible. WDYT?

[abdnh]

That's reasonable. I forgot about the undo case.