Support Guzzle 7 and maintained Faker

[Jord-JD]

What changed

• supports Guzzle 6 and 7 with bounded major constraints
• replaces abandoned fzaninotto/faker with the maintained drop-in fakerphp/faker
• replaces the abandoned Coveralls package
• retains the PHP 5.5.9 package floor while allowing Composer to select compatible dependency releases
• adds PHP 7.4/PHP 8.5 and Guzzle 6/7 CI

Why

This resolves the compatibility intent of #4 while also removing the runtime dependency that blocks modern PHP.

Validation

• Composer JSON parsed successfully
• git diff --check passed
• GitHub Actions runs the test suite across both supported Guzzle majors