Refactor method signatures to use nullable parameter syntax (#19)

Updated method signatures in test traits to explicitly use nullable types (`?type`) for better consistency and clarity. This ensures type hints properly reflect parameters that can accept `null` as a valid value.

Update cs rules

Update readme

Update requirements

Optimize insertFixture in database test trait

Add RouteTestTrait #1

Fix truncate table for MySQL 8

Fix database table loop

Update dev dependencies

Decouple HttpTestTrait from slim/psr7