Indent guides are wrong with proportional fonts.

[matj1]

I have some code typeset with a proportional font, and I would like to give it indentation guides. But indent guides are too far when they are enabled.

See this document:

#import "@preview/algo:0.3.4": code
#show raw: set text(font: "Fira Sans")

#code(
  indent-guides: 1pt + gray,
  tab-size: 4
)[```rust
pub fn minimal_closed_subspaces(network: &BooleanNetwork) {
    loop {
        match state {
            Some(ref subspace) => {
                let greater = greater_subspaces(subspace, &closed.var_set);
                closed.bdd = closed.bdd.and(&greater.not());
                state = next_sat_val(&closed.bdd, subspace); }
            None => break } }
    Ok(closed) }
```]

tab-size is set correctly, but the indent guides are too far like if a wrong width was used to calculate the indentation.