Fix XML parser callbacks on PHP 8.4

[gorsky87]

Summary

• replace deprecated xml_set_object() usage with direct method callables
• keep XML parsing behavior unchanged while avoiding PHP 8.4 deprecation warnings
• add a regression test that fails if XML parsing emits E_DEPRECATED notices

Root cause

PHP 8.4 deprecates xml_set_object() and expects proper method callables to be passed to the xml_set_*_handler() functions. Passing string method names after removing xml_set_object() causes the parser resource itself to be passed incorrectly, which is the TypeError reported in the issue.

Validation

• vendor/bin/phpunit test/Parser/XmlTest.php
• php -d memory_limit=-1 vendor/bin/phpunit
• PHP 8.4 container smoke test with XML parser deprecations converted to exceptions

Fixes #13.