feat(process-executor): stub plugin-facing execute_async_php path

A plugin can reach ProcessExecutor::executeAsync() through the
rust-proxy stub, which resolves with a real Symfony Process instance
that can't be reconstructed on the Rust side (its state is tied to
whichever process calls proc_open(), and it refuses serialization).
Add execute_async_php() as a todo!() stub, documented as a dual-
instantiation split in plugin-class-classification.md: Rust-internal
callers keep using execute_async(), while the plugin path must forward
spawning to the PHP child once the RPC channel exists.

0 files changed, 0 insertions, 0 deletions