update pathfinder args for psis_resample and lp_calculate

[SteveBronder]

Submission Checklist

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

Summary

Adds the psis_resample and calculate_lp arguments to pathfinder

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(this will be you or your assignee, such as a university or company):
Simons Foundation

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/)

[avehtari]

There is a confusing warning after running with psis_resample=FALSE

> pth6 <- model6$pathfinder(data = standata6, init=0.1, num_paths=10, single_path_draws=40,
                          history_size=50, max_lbfgs_iters=100, psis_resample=FALSE)
> pdraws6 <- pth6$draws()
Warning message:
In read_csv_metadata(output_file) : NAs introduced by coercion

[avehtari]

The returned number of draws per path is always at least 25

> pth8rhs <- model8rhs$pathfinder(data = standata8, init=0.1,
                                num_threads=1,
                                num_paths=1, single_path_draws=10, draws=10,
                                history_size=50, max_lbfgs_iters=100,
                                psis_resample=FALSE)
> ndraws(pth8rhs$draws())
25

The returned number of draws should be what the user asks

EDIT: I guess this is CmdStan/Stan bug, but reported now here as part of my testing

[avehtari]

lp_calculate=FALSE seems to work in a sense that I see NaN's, but surprisingly I don't see any performance difference with Birthdays models. I guess I need to test with a bigger data.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cd7b94b) 88.28% compared to head (bc0f18a) 88.32%.

❗ Current head bc0f18a differs from pull request most recent head 89c3375. Consider uploading reports for the commit 89c3375 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #903      +/-   ##
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+ Coverage   88.28%   88.32%   +0.03%     
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  Files          12       12              
  Lines        4534     4548      +14     
==========================================
+ Hits         4003     4017      +14     
  Misses        531      531              

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