task: #3579390: Bump PHPStan to level 5 and fix errors

Derek Wrightrequested to merge
issue/pathologic-3579390:3579390-phpstan-level-5 into 2.0.x

task: #3579390: Add remaining PHPStan warnings to phpstan-baseline.neon, changing _pathologic_replace() is scary

Closes #3579390

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