Add a Testo suite next to a restored (and tuned) PHPUnit suite

[roxblnfk]

Companion PR to the benchmark write-up "What's faster?" — it puts the three runners side by side in this repo so the numbers can be reproduced.

The Tempest suite in tests/ is left untouched. Two more suites run the same tests through a different runner:

Folder	Runner	Namespace	Command
tests/	tempest/testing	Tests\	composer test
phpunit/	PHPUnit 13	Tests\PHPUnit\	composer phpunit
testo/	Testo	Tests\Testo\	composer testo

Running

composer install
cp .env.example .env   # fill in DB / Redis credentials

composer test          # tempest test  -> tests/
composer phpunit       # phpunit       -> phpunit/
composer testo         # testo run     -> testo/