Remove all cast_ref_to_mut

[wenyuzhao]

Transmuting a const ptr to a mutable ptr has become a hard compile error since rustc 1.72 rust-lang/rust#111567

We need to consider refactoring and removing all the cast_ref_to_mut related code before upgrading to 1.72.

[Manishearth]

Note: if the shared mutation is a part of the design, and you can prove that the shared mutation never overlaps with any reads, the way to avoid that UB is to store lxr etc as UnsafeCell<LXR<...>> and use the UnsafeCell methods to get mutable references. Rust does allow for the C model of shared mutation using cell types, however there is still UB possible with UnsafeCell.

I recommend trying to refactor it such that unsafe is not needed.

(or slap a RefCell on everything you want to mutate here and pay the runtime cost)

[playXE]

This PR fixes UB using NonNull<> and UnsafeCell where appropriate everywhere: #893