Run tests on PHP 8.4 and update test environment + PCOV to avoid segfault with Xdebug 3.4.2

[PaulRotmann]

Builds on top of #269, #270 and reactphp/socket#323.
Also had to remove ext-ev from default extensions, install it explicitly based on PHP version.

[PaulRotmann]

I refactored the CI workflow using a new approach with a ternary expression to conditionally include the appropriate ev extension version based on PHP. This greatly simplified the setup and made many of the previous redundant changes unnecessary.

The tests now run cleanly in GitHub Actions with ev installed properly on all targeted PHP versions. Thanks for the feedback, happy to adjust further if needed!

[clue]

@PaulRotmann Thanks for the update, changes look much cleaner now, all LGTM 👍