This pull request modifies the `BytesLoader` implementation for
`FileLoader` in `crates/egui_extras/src/loaders/file_loader.rs` to
improve thread safety and handle unexpected states more gracefully.
### Changes to thread safety and state handling:
* Updated the cache logic to check if the `uri` exists in the cache
before inserting the result. If the `uri` is not found, a log message is
added to indicate the loading was canceled. This change prevents
overwriting cache entries unexpectedly.
* Closes <https://github.com/emilk/egui/issues/6755>
* [x] I have followed the instructions in the PR template
ab9f55ab01