Unable to configure RetryConfig when using parse_url_opts

We're using object_store's `parse_url_opts` to create object stores from URLs like s3://bucket/path. However, there doesn't seem to be a way to configure RetryConfig when using this approach.

Current code: https://github.com/Barre/ZeroFS/blob/c8e6da2443f8b767b990942e3efcea17d42bef7e/src/main.rs#L202-L205

**Problem**

- `parse_url_opts` returns `Box`
- The `with_retry` method is only available on concrete implementations (e.g., `AmazonS3Builder`), not on the trait object
- We need to configure retry behavior but can't access the builder pattern after using `parse_url_opts`

Start at the parse_url_opts entry point and review how it produces a Box, then compare that with the concrete builder APIs such as AmazonS3Builder and with_retry. Determine how RetryConfig should be exposed for URL-created stores; done means retry behavior can be configured through this approach and the behavior is covered by tests.

Written by the indexing model from the issue text.