How to get to the East and West world now that they're blocked by cursed rock?
I'm going to give you two important hints that might make this still reasonably possible while not taking enormous amounts of damage:
There are wands that allow you to teleport.
When a twin spell mod combines two spells of diffrent projectile speed, the second projectile's speed will match that of the first one.
If you don't like puzzles and want a direct answer, view the spoiler tags below for an explicit example solution.
Combine Black Hole with a fast projectile spell, and the result is a fast-moving Hole that can eat up much more rock per use. Add in fast projectile mod as well and you've got something that can eat through several screens worth of rock with one click. A wand that fires two (or more) spells at the same time might also work.
Combining (1) and (2) you can tunnel through the edge of the world far more easily having these two wands (or having edit wands everywhere and the required spells in your inventory).
After ambrosia was added, luminous drill became viable again.
Pour about half of the flask into the tunnel, and dig at about 30° downwards:
It takes a lot of time, since you need to make the floor as smooth as possible to avoid losing ambrosia in the crevices.