Use Environment as the exec and fs gateway

Co-authored-by: Codex <noreply@openai.com>

codex-rs/exec-server/src/server/filesystem.rs

@@ -36,7 +36,7 @@ pub(crate) struct ExecServerFileSystem {
 impl Default for ExecServerFileSystem {
     fn default() -> Self {
         Self {
-            file_system: Arc::new(Environment.get_filesystem()),
+            file_system: Environment::default().get_filesystem(),
         }
     }
 }