Enhance CI workflow with PHP compatibility checks and coverage updates

[adbario]

This pull request introduces several improvements and refinements across the codebase, documentation, and developer tooling for the project. The main focus is on enhancing static analysis, code quality, and documentation accuracy, while also updating the CI workflow and adding developer conveniences. Below are the most significant changes grouped by theme.

Static Analysis, Linting, and Testing Improvements:

• Increased PHPStan analysis level to 8, included phpstan-phpunit extensions, and adjusted configuration to better match the project's needs (phpstan.neon.dist, composer.json). [1] [2] [3]
• Added PHP compatibility checks and improved code style enforcement by including phpcompatibility/php-compatibility and related plugins, and updated phpcs.xml.dist to enforce compatibility with PHP 7.4+ (composer.json, phpcs.xml.dist). [1] [2]
• Enhanced PHPUnit configuration to fail on warnings and risky tests, updated schema, and improved coverage settings (phpunit.xml.dist). [1] [2]
• Refined and expanded the test suite to cover new behaviors, such as handling of non-array values in push, integer key handling in set, and more granular count behaviors (tests/DotTest.php). [1] [2] [3] [4] [5]

Continuous Integration and Workflow Updates:

• Improved the GitHub Actions workflow: added concurrency control, explicit permissions, switched to composer install action, improved test matrix, and modernized coverage reporting with Coveralls (.github/workflows/tests.yml). [1] [2]
• Updated .gitattributes to exclude composer.lock from exports, reducing unnecessary files in distribution (.gitattributes).

Codebase Enhancements and Bug Fixes:

• Improved the Dot class: fixed type annotations, improved handling of non-string keys in set, clarified behavior of push and count, and added PHPStan ignore for a specific type inference issue (src/Dot.php). [1] [2] [3] [4] [5] [6] [7]
• Enhanced the dot() helper to allow calling without arguments (src/helpers.php).

Documentation Updates:

• Clarified documentation in README.md for count, push, and replace methods, updated PHP code examples for modern syntax, and improved instructions for static analysis and JSON output options (README.md). [1] [2] [3] [4] [5] [6] [7]

Developer Tooling:

• Added a .editorconfig for consistent editor settings and expanded Makefile with more targets and improved phony handling (.editorconfig, Makefile). [1] [2]