Our closure capture chapter is wrong

[Veykril]

It was written with the old (pre-2021 edition) capturing rules in mind, rewriting it should also allow us to get rid of unique borrows which are not necessarily user facing

[PLeVasseur]

Hi @Veykril -- is this still relevant? Maybe @tshepang would also know, so tagging him here too.

[mattheww]

NB the Reference update for the 2021 edition changes to closure capturing was rust-lang/reference#1521 (merged in December 2024).