Validate user-provided pit at the entry point

[utkarshpawade]

Fixes #503

Summary

Validates user provided pit argument immediately when it is provided

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.18%. Comparing base (009d7ec) to head (29820db).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
R/ppc-loo.R	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #504      +/-   ##
==========================================
- Coverage   99.19%   99.18%   -0.02%     
==========================================
  Files          35       35              
  Lines        6115     6113       -2     
==========================================
- Hits         6066     6063       -3     
- Misses         49       50       +1     

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[florence-bockting]

Hi @utkarshpawade, thanks for the PR. I provided a small discussion about your observation in the corresponding Issue.

Probably you could adjust the PR accordingly.

[Copilot]

Pull request overview

This PR addresses #503 by moving validation of user-supplied LOO-PIT (pit) inputs earlier in the ppc_loo_* pipeline to prevent downstream failures during boundary-corrected KDE processing.

Changes:

• Validate user-provided pit at the start of ppc_loo_pit_data() and ppc_loo_pit_qq() via validate_pit().
• Update unit tests to assert errors for invalid user-provided pit values.
• Modify .kde_correction() by removing the prior infinite-value filtering and adding an abort when the convolution result is entirely NA.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
R/ppc-loo.R	Routes user-supplied pit through validate_pit() and adjusts .kde_correction() failure handling.
tests/testthat/test-ppc-loo.R	Replaces .kde_correction() warning test with entry-point validation error tests for ppc_loo_pit_data() / ppc_loo_pit_qq().
NEWS.md	Documents the new pit validation behavior for ppc_loo_pit_data() and ppc_loo_pit_qq().

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