Add php-src PHPT compatibility runner

[TrixNEW]

What do you want?

Run PHP's official PHP 8.4.16 test suite against zphp.

Tasks
Implement enough PHPT parsing to support:

• --FILE--
• --EXPECT--
• --EXPECTF--
• --EXPECTREGEX--
• --INI--
• --ENV--
• --SKIPIF--
• --CLEAN--
  Import tests from the PHP 8.4.16 tag.
  Start with:
• Zend/tests
• tests/lang
• ext/standard/tests
• ext/json/tests
• ext/pcre/tests
• ext/spl/tests
• ext/reflection/tests
• ext/date/tests
• ext/hash/tests
  Produce pass/fail/skip statistics.
  Add a CI regression threshold so compatibility cannot silently decrease.

Done when:
zphp can continuously compare itself against upstream PHP 8.4.16 PHPT behavior.

Why does it belong here?

The custom tests are useful but cannot cover the thousands of edge cases tested by php-src.

Alternatives considered

No response

[nvms]

PHP's existing runner could run these tests against zphp since it can select another executable, so I don't see a reason to write a separate PHPT parser.

The obstacle is config support. The runner passes PHP command-line options and settings that zphp doesn't fully implement yet. Ignoring those would make the results unreliable. I'm leaving this open until that support is in place, with PHP 8.5 as the target, and not specifically 8.4.16.