Add multithreading and stanc_optimization arguments to CmdStanModel

[amas0]

Submission Checklist

• Run unit tests
• Declare copyright holder and open-source license: see below

Summary

This adds two new boolean keyword arguments to CmdStanModel: multithreading and stanc_optimizations. These are included as a short-hand way to enable the common compilation options STAN_THREADS and O1 optimizations in stanc.

Also updates workflow documentation on model compilation to mention these new options and reflect recent removal of deprecated compile options.

Resolves #837 and #836.

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): myself

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)

[WardBrian]

Thanks for tackling! A couple minor comments:

[WardBrian]

Should we add these to compilation.compile_stan_model do you think? That is ultimately what gets called by the constructor, but it is also available to users.

[amas0]

I considered it when implementing this.

It'd be an easy change, but I wasn't sure I liked the idea of adding the same keyword args to both CmdStanModel and compile_stan_model every time we wanted to add a shorthand flag. I also perceived compile_stan_model to be a bit lower-level.

I don't feel that strongly about it. Happy to make the change if you think it'd be useful.

[WardBrian]

Seems fair — it’s easy enough to add them later if we desire