Changes

Fix incorrect Tricky Trials potion durations via UpgradeManager migration

Warriorrrr's commit (fb6aebcaa) corrected the default potions.yml shipped
with the plugin (splash: 2500->3600, lingering: 3000->900), but existing
server installs still had the old incorrect values.

This adds a one-time UpgradeManager migration (FIX_TRICKY_TRIALS_SPLASH_POTION_DURATIONS)
that auto-patches existing potions.yml on first server startup after updating.
The migration only corrects exact-match bad values; user-customized durations
are intentionally left untouched. Absent potion keys are silently skipped.

- Add UpgradeType.FIX_TRICKY_TRIALS_SPLASH_POTION_DURATIONS
- Implement PotionConfig.fixTrickyTrialsPotionDurations() + patchTrickyTrialsDurations()
- Gate migration in PotionConfig.loadPotions() via shouldUpgrade()
- Add 13 unit tests covering all migration paths in PotionConfigTest
 (commit: 366a512)