fix: prevent worker starvation after max_execution_time restarts
Disable the execution timer in frankenphp_worker_request_shutdown() to
prevent stale timers from firing between requests. Also fix evaluation
order in frankenphp_handle_request() to check for shutdown before calling
frankenphp_worker_request_startup().
Fixes #2205
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>