* PHP 8.1 warning fixes
Added #[\ReturnTypeWillChange] or appropriate return values
Typed parameters where appropriate
* Fixing unit tests to run without warnings
* Update to more reasonable versions of PHP and PHPUnit (was missing PHPUnit 8)
* mb_check_encoding param 1 can not be null
* Fix SeekingData class for 8.1
* Update tests to not polute the temp directory
* Revert PHP contrant
* Tabs to spaces
* Use Symfony\Component\VarDumper\Cloner\Data\SeekingData instead of local backported version
Avoids Fatal error: Declaration of DebugBar\DataFormatter\VarDumper\SeekingData::seek($key) must be compatible with Symfony\Component\VarDumper\Cloner\Data::seek(string|int $key): ?static
Co-authored-by: Barry vd. Heuvel <barryvdh@gmail.com>
