feat: codex-linux-sandbox standalone executable (#740)

This introduces a standalone executable that run the equivalent of the
`codex debug landlock` subcommand and updates `rust-release.yml` to
include it in the release.

The idea is that we will include this small binary with the TypeScript
CLI to provide support for Linux sandboxing.

codex-rs/cli/src/seatbelt.rs

@@ -1,7 +1,7 @@
 use codex_core::exec::create_seatbelt_command;
 use codex_core::protocol::SandboxPolicy;
 
-pub(crate) async fn run_seatbelt(
+pub async fn run_seatbelt(
     command: Vec<String>,
     sandbox_policy: SandboxPolicy,
 ) -> anyhow::Result<()> {