[4.x] Add dependsExternal (depend on tests in external test files)

[Ajility97]

What

• Bug Fix
• New Feature

Description

The existing depends() method does not support dependencies across test files. In larger test suites, it can be useful to reuse values returned by tests defined in other test cases.

This PR introduces a chainable dependsExternal() method, which allows a test to depend on tests defined in another test file. It accepts the target test file as the first argument, followed by one or more dependency test names as variadic arguments.

Example usage:

test('depends on tests in an external file', function (string $first, string $second) {
    expect($first)->toBe('first');
    expect($second)->toBe('second');
})->dependsExternal('Tests\\Features\\Depends', 'first', 'second');

Related:

#969
#1059
#1054