Windows Sandbox: Show Everyone-writable directory warning (#6283)

Show a warning when Auto Sandbox mode becomes enabled, if we detect
Everyone-writable directories, since they cannot be protected by the
current implementation of the Sandbox.

This PR also includes changes to how we detect Everyone-writable to be
*much* faster

codex-rs/Cargo.lock

@@ -1452,6 +1452,7 @@ dependencies = [
  "codex-login",
  "codex-ollama",
  "codex-protocol",
+ "codex-windows-sandbox",
  "color-eyre",
  "crossterm",
  "diffy",