[donatj]

This package lacks static analysis. Array contracts and PHP compatibility problems can therefore reach releases unchecked.

Changes:

• Add PHPStan 2.3.1 as a development dependency.
• Add a level-9 configuration for source files.
• Run PHPStan in continuous integration.
• Define precise array contracts in public PHPDoc.
• Make array flattening preserve values that cannot be used as array keys.
• Regenerate the README and add a regression test.

Validation:

• composer validate --strict --no-check-publish
• composer install --dry-run
• vendor/bin/phpstan analyse
• vendor/bin/phpunit --do-not-cache-result
• vendor/bin/mddoc --dry-run
• php -l src/array.php
• Ruby YAML parsing
• git diff --check