app-server: Add streaming and tty/pty capabilities to command/exec (#13640)

* Add an ability to stream stdin, stdout, and stderr
* Streaming of stdout and stderr has a configurable cap for total amount
of transmitted bytes (with an ability to disable it)
* Add support for overriding environment variables
* Add an ability to terminate running applications (using
`command/exec/terminate`)
* Add TTY/PTY support, with an ability to resize the terminal (using
`command/exec/resize`)

codex-rs/app-server/src/lib.rs

@@ -58,6 +58,7 @@ use tracing_subscriber::util::SubscriberInitExt;
 mod app_server_tracing;
 mod bespoke_event_handling;
 mod codex_message_processor;
+mod command_exec;
 mod config_api;
 mod dynamic_tools;
 mod error_code;