Add Support for Background Sessions and Delegate-Based API

### Is your feature request related to a problem? Please describe.

The current Box SDK library does not support background sessions. An error is thrown at [NetworkClient.swift#L86](https://github.com/box/box-swift-sdk-gen/blob/a6b5793ab4053f9b55b840245ad07c9e3fdae344/Sources/Networking/NetworkClient.swift#L86) with the message: `Completion handler blocks are not supported in background sessions. Use a delegate instead.`

Additionally, the library does not differentiate between request types for creating background-compatible upload tasks, which are necessary for handling uploads in the background. This lack of support limits the SDK's utility for apps that need to perform background uploads (and downloads).

### Describe the solution you'd like

I would like the SDK to support background sessions by transitioning from a callback-based API to a delegate-based API. Specifically, there should be differentiation in request creation to use [`URLSessionUploadTask`](https://developer.apple.com/documentation/foundation/urlsessionuploadtask), as this type of task allows for uploads in the background, unlike data tasks.

This change would require modifying the API to accept file `URL`s instead of `InputStream`s to comply with the requirements of `URLSessionUploadTask` and enable background operation.

### Describe alternatives you've considered

I have already forked the repository and made the necessary changes to support background sessions by:

- Refactoring the API to use delegates instead of callbacks.
- Differentiating request creation to use `networkSession.session.uploadTask()` as well.
- Switching from `InputStream` to file `URL`s for upload tasks.

My changes can be viewed here: https://github.com/tobihagemann/box-swift-sdk-gen/compare/a6b5793ab4053f9b55b840245ad07c9e3fdae344...b2bb9db3b4fc5e86807f3c5043bedcab9fdf48f7

However, since this project appears to be generated, integrating these changes directly through a PR may not be practical due to the extent of the modifications, resulting in hundreds of lines of code changes.