feat: re-add simplify= to print.compare.loo (#366)

[LeonidasZhak]

Summary

Re-adds a simplify parameter to print.compare.loo() (default TRUE), addressing #366.

When simplify = FALSE, the full comparison table is printed including pointwise ELPD, LOOIC/WAIC, and their standard errors for each model. This restores functionality that was available in previous versions of loo.

Changes

• R/loo_compare.R: Add simplify parameter to print.compare.loo() with roxygen documentation
• man/loo_compare.Rd: Regenerated by roxygen2
• man/loo-package.Rd: Minor roxygen2 update

Example

comp <- loo_compare(loo1, loo2, loo3)

# default (simplified) output
print(comp)

# full output with all ELPD/LOOIC columns
print(comp, simplify = FALSE)

Testing

• All existing tests pass: [ FAIL 0 | WARN 0 | SKIP 2 | PASS 1144 ]
• Manual verification that simplify = TRUE (default) produces identical output to current behavior
• Manual verification that simplify = FALSE correctly displays all available estimate columns

Closes #366

[codecov-commenter]

Codecov Report

❌ Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.49%. Comparing base (286263d) to head (beec4b6).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
R/loo_compare.R	12.50%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #369      +/-   ##
==========================================
- Coverage   92.70%   92.49%   -0.22%     
==========================================
  Files          31       31              
  Lines        3029     3037       +8     
==========================================
+ Hits         2808     2809       +1     
- Misses        221      228       +7     

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[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if beec4b6 is merged into master:

• ✔️loo_function: 1.89s -> 1.89s [-0.6%, +0.33%]
• ✔️loo_matrix: 1.7s -> 1.7s [-0.58%, +0.67%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[florence-bockting]

Thank you @LeonidasZhak for opening this PR. We had some discussion about whether to include/exclude this argument from loo_compare in this PR.
Therefore, we (@avehtari, @jgabry) need probably to discuss first how we want to handle this aspect and then we will come back to your PR.

[florence-bockting]

Thanks again @LeonidasZhak for the PR.
Please read our AI contribution policy and disclose any use of AI.
Additionally, please add tests for any changes you make to functions; stating "manual verification" is not sufficient.
Finally, please avoid making changes to files unrelated to this PR, as was done in loo-package.Rd.