rewind random source and recreate pruned rooms

[ssube]

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Find a way to rewind the random number source and recreate pruned rooms from the same template, to prevent major differences when backtracking and revisiting a room.

[ssube]

This will require, at least:

• recording when the room was first visited (by PRNG tick, not just turn)
• which template was used (potentially re-rollable once the PRNG has been (re)wound)
• which actors have left (to prevent spawning multiple copies, esp if they should be unique)
• which items have been taken (to prevent farming items)

That data will still take up some space in the world state, hopefully less than the active room and its contents.

If stable recreation is an option, the main benefit of removing rooms will be to reduce step invocations, rather than reducing save size.