refactor: fix codeigniter.modelArgumentType errors

[paulbalandan]

Description

1. Save the model call from instantiating non class-strings.
2. Added Tests\Support\Models namespace as known model namespaces.
   3. Adding Shield's namespace is not enough since PHPStan must know the class do exist, so we required shield as a dev dependency.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[paulbalandan]

It seems the approach of requiring shield brings a lot of testing errors. Skipping that solution for now.