* The Messenger: transition rando
* remove unused import
* always link both directions for plando when using coupled transitions
* er_type was renamed to randomization_type
* use frozenset for things that shouldn't change
* review suggestions
* do portal and transition shuffle in `connect_entrances`
* remove some unnecessary connections that were causing entrance caching collisions
* add test for strictest possible ER settings
* use unittest.skip on the skipped test, so we don't waste time doing setUp and tearDown
* use the world helpers
* make the plando connection description more verbose
* always add searing crags portal if portal shuffle is disabled
* guarantee an arbitrary number of locations with first connection
* make the constraints more lenient for a bit more variety
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