[codex-rs] Add rust-release action (#671)

Taking a pass at building artifacts per platform so we can consider
different distribution strategies that don't require users to install
the full `cargo` toolchain.

Right now this grabs just the `codex-repl` and `codex-tui` bins for 5
different targets and bundles them into a draft release. I think a
clearly marked pre-release set of artifacts will unblock the next step
of testing.

codex-rs/Cargo.toml

@@ -10,3 +10,9 @@ members = [
     "repl",
     "tui",
 ]
+
+[workspace.package]
+version = "0.1.0"
+
+[profile.release]
+lto = "fat"