Prepare loo version 3.0.0

[florence-bockting]

Description

This PR prepares the transition to loo v3.0.0.

This branch should be kept in sync with master as much as possible, and should serve as the base branch for merging any PRs considered part of loo v3.0.0, including any refactoring planned for this release.

Comments, questions, and other discussion arising during the refactoring and preparation of loo v3.0.0 should be collected here.

For loo v3.0.0 we consider among other to tackle the following problems/tasks

• implementation of pred_measure (Adding pred_measure feature #363)
• parallelization of loo with mirai and mori (Parallelization of loo using mirai and mori #378)
• improved warning/messaging behavior (Improve warnings and messages behavior #353)
• handling of r_eff in loo.function (loo.function should not require a r_eff argument #106, Change n_eff to ESS #192)
• subsetting psis object (Feature Request: public subset() method for psis objects #343)
• general refactoring to clean-up the backend

[florence-bockting]

Tagging @jgabry, @avehtari, and @VisruthSK so you are aware of this PR and the process.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.70%. Comparing base (720bb30) to head (5cd282e).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #379   +/-   ##
=======================================
  Coverage   92.70%   92.70%           
=======================================
  Files          31       31           
  Lines        3029     3029           
=======================================
  Hits         2808     2808           
  Misses        221      221           

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[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 5cd282e is merged into master:

• ✔️loo_function: 1.88s -> 1.88s [-0.49%, +0.51%]
• ✔️loo_matrix: 1.74s -> 1.74s [-0.49%, +0.72%]
  Further explanation regarding interpretation and methodology can be found in the documentation.