Support V0.12

[iandol]

Typst V0.12 causes a bunch of warnings with lapreprint now, e.g.:

warning: `locate` with callback function is deprecated
    ┌─ lapreprint.typ:89:10
    │  
 89 │       header: locate(loc => {
    │ ╭─────────────^
 90 │ │       if(loc.page() == 1) {
 91 │ │         let headers = (
 92 │ │           if (open-access) {smallcaps[Open Access]},
    · │
100 │ │       }
101 │ │     }),
    │ ╰──────^
    │  
    = hint: use a `context` expression instead

warning: `show par: set block(spacing: ..)` has no effect anymore
    ┌─ lapreprint.typ:311:1
    │
311 │   show par: set block(spacing: 2em)
    │   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    │
    = hint: write `set par(spacing: ..)` instead
    = hint: this is specific to paragraphs as they are not considered blocks anymore

warning: `locate` with callback function is deprecated
    ┌─ lapreprint.typ:138:21
    │  
138 │     show heading: it => locate(loc => {
    │ ╭───────────────────────^
139 │ │     // Find out the final number of the heading counter.
140 │ │     let levels = counter(heading).at(loc)
141 │ │     set text(10pt, weight: 400)
    · │
176 │ │     ]
177 │ │   })
    │ ╰────^
    │  
    = hint: use a `context` expression instead

warning: `counter.display` without context is deprecated
    ┌─ lapreprint.typ:307:26
    │
307 │     #strong[#it.supplement #it.counter.display(it.numbering)]: #it.body
    │                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    │
    = hint: use it in a `context` expression instead

warning: calling `counter.final` with a location is deprecated
    ┌─ lapreprint.typ:118:53
    │
118 │               #counter(page).display() of #locate((loc) => {counter(page).final(loc).first()})
    │                                                             ^^^^^^^^^^^^^^^^^^^^^^^^
    │
    = hint: try removing the location argument

These are all warnings so do not yet stop compilation.