buildTypstProjectLocal various issues

[loqusion]

buildLocalTypstProject is currently implemented with import from derivation. This has some mildly unfortunate consequences:

• It doesn't work when allow-import-from-derivation is switched from the (current) default to false
• buildTypstProjectLocal relies on running a shell script for side effects (i.e. copying to current directory), but since that shell script can't realize the buildTypstProject derivation output itself, it relies on nix run, direnv reload etc.
  • For instance, adding the script derivation to a dev shell's packages and running it will simply copy a possibly-stale derivation result