Fix expose_functions under 2.32

[andrjohns]

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

Fixes compatibility with cmdstan 2.32 for exposing functions

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):
Andrew Johnson

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)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[codecov-commenter]

Codecov Report

Merging #769 (0b5b201) into master (ab30e07) will decrease coverage by 2.05%.
The diff coverage is 83.33%.

❗ Current head 0b5b201 differs from pull request most recent head b189bc8. Consider uploading reports for the commit b189bc8 to get more accurate results

@@            Coverage Diff             @@
##           master     #769      +/-   ##
==========================================
- Coverage   88.26%   86.22%   -2.05%     
==========================================
  Files          12       12              
  Lines        4117     4130      +13     
==========================================
- Hits         3634     3561      -73     
- Misses        483      569      +86     

Impacted Files	Coverage Δ
R/fit.R	96.06% <ø> (ø)
R/utils.R	72.34% <82.75%> (-2.23%)	⬇️
R/model.R	90.45% <100.00%> (-0.14%)	⬇️

... and 3 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[andrjohns]

@rok-cesnovar this is ready for a look. The windows test failures here (messages being printed when not interactive()) are the same ones from master and need to be sorted separately

[rok-cesnovar]

Awesome, thanks!

[jgabry]

Thanks @andrjohns!