Remove unnecessary usages of `WorldCell` API

[alice-i-cecile]

Per #3939, there are a number of places in the code base where WorldCell (used to get split mutable access to the World) is used but is not needed.

This leads to pointlessly panic-prone code that will be slower, harder to read and more blocking.

To complete this issue, extract and rebase the changes from #3939 (other than removing the WorldCell API).