Record Windows MXC availability (#42094)

## What changed

- Probe whether the native Windows MXC process security environment is usable
  when selecting a sandbox.
- Emit `codex.windows_mxc.available` at most once per process, labeled with the
  probe result.
- Add the MXC workspace dependencies for Cargo and Bazel, and pin
  `tracelogging` to a version compatible with the GNU Windows toolchain.

GitOrigin-RevId: d7cfeed6f0333feda5764e1ee44fe5bbd50f9a58

codex-rs/deny.toml

@@ -313,6 +313,7 @@ allow-git = [
     "https://github.com/dzbarsky/rules_rust",
     "https://github.com/helix-editor/nucleo.git",
     "https://github.com/juberti-oai/rust-sdks.git",
+    "https://github.com/microsoft/mxc",
     "https://github.com/openai-oss-forks/crossterm",
     "https://github.com/openai-oss-forks/tokio-tungstenite",
     "https://github.com/openai-oss-forks/tungstenite-rs",