THRIFT-6023: Add HTTP transport support to PHP cross-tests

[sveneld]

Adds HTTP transport support to the PHP entry of the cross-test matrix. PHP was the only major-language entry stuck on buffered/framed while Python, Go, Node, C++, Java, Lua, Dart, JS, D, and Haskell already declare http and verify HTTP interop.

Server — TestServer.php detects --transport=http in CLI mode and pcntl_exec()s into PHP's built-in web server (php -S 127.0.0.1:$port TestServer.php). The same script re-enters under SAPI cli-server, reads the request via TPhpStream from php://input, dispatches it through the existing processor, and writes the response to php://output. The original -d flags from the launcher cmdline (e.g. -dextension=thrift_protocol.so) are preserved by parsing /proc/self/cmdline, so the accel extension and sockets stay loaded under the spawned server too. The cross-runner's socket.connect_ex readiness probe works because php -S TCP-binds the port immediately.

Client — TestClient.php gains an if ($MODE == 'http') branch that uses TPsrHttpClient (added in THRIFT-6010) against http://127.0.0.1:$port/. TPsrHttpClient buffers internally, so no TBufferedTransport/TFramedTransport wrapping.

tests.json — adds "http" to PHP server and client transports; bumps client timeout from 6s → 10s to absorb HTTP overhead.

composer.json — adds guzzlehttp/guzzle: ^7.8 to require-dev so the PSR-18 auto-discovery in TPsrHttpClient resolves a concrete HTTP client at cross-test time.

JIRA: THRIFT-6023. Draft until cross-test CI validates the new php↔php / php↔py3 / php↔go HTTP matrix cells.

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