Prefer just test over cargo test in docs (#23910)

`cargo test` for the core and other crates fails on a fresh macOS
checkout without the right stack size variable. This change encourages
using the just test command that sets the environment up correctly.

As a bonus, this should encourage agents to get more benefit out of
nextest's parallel execution.

codex-rs/app-server/README.md

@@ -1950,5 +1950,5 @@ For server-initiated request payloads, annotate the field the same way so schema
 5. Verify the protocol crate:
 
    ```bash
-   cargo test -p codex-app-server-protocol
+   just test -p codex-app-server-protocol
    ```

codex-rs/core/tests/suite/live_cli.rs

@@ -2,7 +2,8 @@
 
 //! Optional smoke tests that hit the real OpenAI /v1/responses endpoint. They are `#[ignore]` by
 //! default so CI stays deterministic and free. Developers can run them locally with
-//! `cargo test --test live_cli -- --ignored` provided they set a valid `OPENAI_API_KEY`.
+//! `just test -p codex-core --test all --run-ignored only live_cli` provided they set a valid
+//! `OPENAI_API_KEY`.
 
 use assert_cmd::prelude::*;
 use predicates::prelude::*;

codex-rs/utils/pty/README.md

@@ -60,5 +60,5 @@ Use `spawn_pipe_process_no_stdin` to force stdin closed (commands that read stdi
 Unit tests live in `src/lib.rs` and cover both backends (PTY Python REPL and pipe-based stdin roundtrip). Run with:
 
 ```
-cargo test -p codex-utils-pty -- --nocapture
+just test -p codex-utils-pty --no-capture
 ```