Decouple Excpect from PHPUnit / maintain compatibility

[smnandre]

Introducing a custom AssertionException and a new ExpectDecorator class to decouple from and still be compatible with PHPUnit.

Assertion Counting Integration:

• Replaced all usages of PHPUnit\Framework\AssertionFailedError with Playwright\Assertions\Failure\AssertionException in Expectation.php and Expect.php
• Added a new ExpectDecorator class that wraps the Expect class and automatically increments PHPUnit assertion count when available
• Updated the expect() method in PlaywrightTestCaseTrait to return an instance of ExpectDecorator instead of Expect

[codecov]

Codecov Report

❌ Patch coverage is 0% with 80 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/Testing/ExpectDecorator.php	0.00%	71 Missing ⚠️
src/Testing/Assert/Expectation.php	0.00%	4 Missing ⚠️
src/Testing/Expect.php	0.00%	4 Missing ⚠️
src/Testing/PlaywrightTestCaseTrait.php	0.00%	1 Missing ⚠️

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