Require PHP 8.4, replace Psalm with PHPStan, upgrade Valinor to 2.x, remove PSL

[loevgaard]

Summary

• PHP >= 8.4: bumped the platform requirement; CI now tests PHP 8.4 and 8.5 (lowest + highest deps). symfony/options-resolver trimmed to ^6.4 || ^7.0 || ^8.0.
• Psalm → PHPStan: setono/code-quality-pack ^3.4 brings PHPStan 2.x with strict rules, PHPUnit and webmozart-assert extensions. New phpstan.dist.neon at level max (no baseline), includes Valinor's bundled PHPStan extension so the array-shape mapping in Parser stays fully typed. All @psalm-* annotations converted to @phpstan-* equivalents or made redundant by inline narrowing.
• Valinor ^2.0: error handling migrated from Messages::flattenFromNode($e->node()) to $e->messages(); the shared MapperBuilder now also sets allowPermissiveTypes() since Valinor 2's strict mode otherwise rejects the mixed block data.
• azjezz/psl removed: the top-level JSON shape validation in Parser::parse() is now done by Valinor mapping to an array shape. InvalidDataException::__construct() consequently accepts CuyZ\Valinor\Mapper\MappingError instead of PSL's AssertException.
• PHPUnit 9 → 11 (via the pack): config migrated to the new schema, annotations converted to attributes, data providers made public static.
• Rector 2.x: config modernized with PHP 8.4 + PHPUnit attribute sets and applied (new new X()->method() chaining, explicit nullable params, etc.).

Behavior notes

• Unknown top-level keys in the EditorJS JSON are now tolerated (PSL's shape() rejected them) — more lenient, forward-compatible with new EditorJS exports.
• phpunit/phpunit is intentionally not a direct dev dependency (provided by the pack); the shadow-dependency finding is ignored in composer-dependency-analyser.php.

Test plan

• vendor/bin/phpunit green on highest and lowest deps (46 tests)
• vendor/bin/phpstan 0 errors at level max on highest and lowest deps
• composer check-style, vendor/bin/rector --dry-run, vendor/bin/composer-dependency-analyser, composer validate --strict, composer normalize --dry-run all clean
• Infection mutation tests run in CI

[codecov]

Codecov Report

❌ Patch coverage is 78.12500% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.91%. Comparing base (9832f76) to head (55782c0).

Files with missing lines	Patch %	Lines
src/Exception/InvalidDataException.php	0.00%	5 Missing ⚠️
src/Exception/MappingErrorException.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                1.x      #24      +/-   ##
============================================
- Coverage     82.41%   81.91%   -0.51%     
- Complexity       83       86       +3     
============================================
  Files            29       29              
  Lines           290      293       +3     
============================================
+ Hits            239      240       +1     
- Misses           51       53       +2     

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