Increase code quality to PHPStan level 7

Problem/Motivation

The module was analysed by PHPStan at level 5, with broad ignoreErrors entries that silenced two whole classes of finding: Unsafe usage of new static and Drupal calls should be avoided in classes, use dependency injection instead. Those entries hid real problems rather than fixing them.

Applying drupal_extension_scaffold v4.18.0 replaced the configuration with level 7 and no such ignores, which exposed 37 errors. The largest group was static \Drupal::service() and static entity calls inside classes, which make the code harder to test and prevent the service container from being used properly.

Steps to reproduce

1. Check out 5.0.x.
2. Run make lint.
3. PHPStan reports 37 errors, and PHPCS reports DrupalPractice.Objects.GlobalClass warnings for the same static calls.

Proposed resolution

Fix the underlying causes rather than adding a baseline file or ignore entries:

• TextimageHooks takes its six services by constructor injection, replacing thirteen static \Drupal::service() calls.
• TextimageFactory, TextimageTextFieldFormatter and TextimageImageFieldFormatter take the entity type manager and call getStorage() at the call site, replacing static ImageStyle::load(), ImageStyle::loadMultiple() and EntityViewDisplay::load() calls.
• Classes that use new static() in a create() factory declare @phpstan-consistent-constructor.
• Missing generics, return types and parameter types are declared.
• FALSE returns from StreamWrapperManager::getTarget(), getScheme() and getViaScheme() are handled instead of assumed.
• Image effect plugin instances are checked with instanceof before their methods are called.
• Outstanding Rector rules are applied.
• Kernel test coverage is added for the hooks, the factory and the path processor, so the code these changes touch is actually exercised.

Remaining tasks

• Review the merge request.
• Decide whether the level should stay at 7 or be pinned lower.

User interface changes

None.

API changes

Constructor signatures change for code that instantiates these classes directly. Plugins and services built through the container are not affected.

• TextimageHooks gains a constructor taking StreamWrapperManagerInterface, ImageFactory, TextimageFactoryInterface, FileSystemInterface, TextimageLogger and ConfigFactoryInterface.
• TextimageFactory::__construct() takes EntityTypeManagerInterface as a public readonly promoted property. The protected $userStorage property is removed.
• TextimageTextFieldFormatter::__construct() and TextimageImageFieldFormatter::__construct() take EntityTypeManagerInterface in place of ImageStyleStorageInterface.
• TextimageInterface::setSourceImageFile() and Textimage::setStyle() keep their behaviour; only type declarations are tightened.

Data model changes

None.