Add HTTP/3 protocol mapping to curl adapter - #19546

Summary

Add support for mapping PSR-7 HTTP protocol versions 3 and 3.0 to CURL_HTTP_VERSION_3 in the curl HTTP client adapter.

The adapter now throws an HttpException with a descriptive message when the required curl constant is not available.

Changes

• Map protocol versions 3 and 3.0 to CURL_HTTP_VERSION_3
• Preserve the existing fallback behavior for unsupported or unspecified protocol versions
• Add test coverage for the HTTP/3 protocol mapping

Testing

The HTTP/3 adapter test passes locally with PHP 8.6.0-dev and an HTTP/3-enabled curl build:

../php-src/sapi/cli/php -d zend.assertions=1 \
    vendor/bin/phpunit \
    tests/TestCase/Http/Client/Adapter/CurlTest.php

Notes

This change covers protocol-version mapping in the curl adapter. It does not perform a live HTTP/3 integration test.

CakePHP's default Request implementation currently relies on Laminas Diactoros, which rejects protocol version 3 in withProtocolVersion(). The test therefore uses a partial mock that returns 3 from getProtocolVersion().

A full test-suite run with PHP 8.6.0-dev also reports an unrelated failure in:

Cake\Test\TestCase\View\Helper\TimeHelperTest::testTimeAgoInWordsOutputTimezone

No date, time, view helper, or internationalization files are changed by this pull request.