Fix native-app socket timeout regression test on macOS

[jmcte]

Context

Review of branch codex/issue-2-ipc-timeouts against origin/main found that the new timeout regression test fails before it reaches the timeout assertion on macOS.

Reproduction

cargo test --manifest-path rust/Cargo.toml socket_request_times_out_when_broker_does_not_reply

Observed failure:

thread 'native_app::tests::socket_request_times_out_when_broker_does_not_reply' panicked at src/native_app.rs:1346:61:
called `Result::unwrap()` on an `Err` value: Os { code: 1, kind: PermissionDenied, message: "Operation not permitted" }

Affected code

rust/src/native_app.rs

The test binds a Unix socket and then calls set_permissions(&socket_path, NATIVE_APP_FILE_MODE). On macOS, fs::set_permissions on the socket path returns EPERM, so the test never exercises the intended hung-broker timeout behavior.

Suggested fix

Create the socket with the desired restrictive mode, for example by applying a temporary restrictive umask around UnixListener::bind, or otherwise avoid chmodding the Unix socket path in the test.

Acceptance criteria

• cargo test --manifest-path rust/Cargo.toml socket_request_times_out_when_broker_does_not_reply passes on macOS.
• The test still verifies that a broker that accepts the socket but does not reply returns Status::CommunicationTimeout within the expected bound.