feat: add PHP 8.3, 8.4 and 8.5 compatibility

[joelmiguelvalente]

PHP 8.3, 8.4 and 8.5 Compatibility

This PR updates jBBCode to work with PHP 8.3, 8.4 and future 8.5 versions.

Changes made

• ✅ Added return types (: string, : void, : bool, : array, : self, etc.)
• ✅ Added property types (string $tagName, array $tokens, ?CodeDefinition $codeDefinition, etc.)
• ✅ Updated InputValidator interface to validate(string $input): bool
• ✅ Fixed syntax errors in SmileyVisitor (extra parenthesis)
• ✅ Fixed namespace in TagCountingVisitor (JBBcode → JBBCode)
• ✅ Improved regex in CssColorValidator (A-z → A-Za-z)
• ✅ Updated Tokenizer with proper types
• ✅ Fixed deprecated setters in CodeDefinition to return : void
• ✅ Updated composer.json (PHPUnit 9.6, PHP 8.3+ requirement)

Backward Compatibility

• PHP 7.4 and below are no longer supported
• Existing code that does not rely on implementation details should continue to work

Tests

All existing unit tests pass with PHP 8.3.

Related Issues

Fixes compatibility with PHP 8.x