Allow --heap-size-hint option to be passed

[MilesCranmer]

This option is really useful for when the Julia garbage collector is doing a bad job. e.g., MilesCranmer/PySR#441, JuliaLang/julia#50673, MilesCranmer/PySR#61.

All of these types of issues seem to be easily fixable if you just tell Julia to use a smaller size hint, so the GC works more aggressively. I find this option extremely useful so we should definitely add it.