Add enforce_residency to requirements (#10263)

Add `enforce_residency` to requirements.toml and thread it through to a
header on `default_client`.

codex-rs/cloud-requirements/src/lib.rs

@@ -315,6 +315,7 @@ mod tests {
                 allowed_sandbox_modes: None,
                 mcp_servers: None,
                 rules: None,
+                enforce_residency: None,
             })
         );
     }