fix(prt): fix release time config, fix logic to nudge particle into cells

[wpbonelli]

Fix two issues with PRT:

1. Release time configuration via stress period options did not work correctly. Settings were not loaded, so configured releases could fail to occur, or fill-forward of previous stress period options fail to stop on an empty period block. Fix the release timing logic and add test cases exercising this.

2. Some logic was missing from a routine used to "nudge" particles' barycentric coordinates slightly into the interior of triangular subcells, causing particles to remain outside the relevant subcell. Add the necessary logic to nudge the particle inside the subcell.

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Checklist of items for pull request

• Replaced section above with description of pull request
• Added new test or modified an existing test
• Ran ruff on new and modified python scripts in .doc, autotests, doc, distribution, pymake, and utils subdirectories.
• Formatted new and modified Fortran source files with fprettify
• Added doxygen comments to new and modified procedures
• Updated develop.toml with a plain-language description of the bug fix, change, feature; required for changes that may affect users
• Removed checklist items not relevant to this pull request