chore!: raise minimum PHP version to 8.2 and modernize tooling

[Levdbas]

Summary

• Modernize the Composer toolchain and development dependencies for PHP 8.2 and later.
• Add Rector configuration and development tooling, and configure Composer to sort packages automatically.
• Refresh CI formatting and GitHub Actions checkout usage while expanding the PHP test matrix through PHP 8.4.
• Add Packagist export-ignore rules for development-only files.
• Update the parent-delegation test for PHPUnit 10 by replacing the removed setMethods() call with onlyMethods() and addMethods().

Breaking Change

• Raise the minimum supported PHP version from 5.4 to 8.2.

Validation

• composer update

• composer validate --no-check-publish

• composer test -- tests/ParentDelegationBuilderTest.php

• composer test

• The focused parent-delegation test passes: 2 tests, 2 assertions.

• The full PHPUnit test suite passes.

Consideration

Don't drop support for PHP 7.4 to 8.1? But I'd would be in favor of bumping this so we can really start modernizing the codebase.

Closing note

I haven't ran Rector yet. I would like to do that based on the outcomes of this PR.