feat: Add EditorConfig, GitHub workflows, update PHP version, PSR-7, …

[muhammetsafak]

…PSR-17, PSR-18, PSR-18 Client Configuration documentation, unit tests, src exclusion in phpunit.xml.dist, refactor Client.php, PSR-17 Factory and Facade classes, add FacadableInterface, unit tests for PSR-7 RequestInterface immutability & Host header sync, tests for ResponseReasonPhraseTable, ResponseRedirect, ServerRequestCreateFromGlobals, ServerRequestNormalizeFiles, StreamDetachPreservesPosition, remove message bag, custom interfaces, update to PSR-7, refactor code, remove deprecated interfaces and methods from Message package, update PSR-7 Uri implementation and ClientConfiguration tests

Summary

Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that changes existing behaviour in an incompatible way)
• 📖 Documentation update
• 🔧 Refactor / internal change (no behaviour change)
• ✅ Tests only
• 🚀 CI / build / tooling

Linked issues

How was this tested?

Breaking changes

Checklist

• Code follows PSR-12 and the project's existing style (PHP-CS-Fixer if available, no warnings)
• declare(strict_types=1); is present in any new PHP files in src/
• Public methods have proper type declarations (parameters and return types)
• Tests cover the change — added new tests or updated existing ones (N/A for docs-only PRs)
• PHPStan passes locally at the level configured in the package
• PHPUnit passes locally (composer test or vendor/bin/phpunit)
• Commit messages follow Conventional Commits
• I have read and agree to the Code of Conduct