php
Update to PHP 8.3
This PR updates the extension for PHP 8.3.
Of note: __assign($arg) has been removed, since I don't think it can work anymore (op_handler doesn't seem to be called with ZEND_ASSIGN_OP, ZEND_ASSIGN_DIM_OP, etc when doing $o = $arg;). Everything else should be working, and all the tests are passing on my machine, except the one that requires patching PHP, which I haven't tried since I don't really know how to do that.
I'm not very familiar with PHP internals, so this is a best effort attempt, from what I've been able to piece together from the php-src repo's git history. I can't tell if any of the changes I've made could cause issues.
I don't really have a use-case for this extension, I just wanted to update it as an excuse to delve more into PHP internals.
