ActiveStorage raw file uploads fail with "An unknown file format not allowed" due filename being lost

## Bug report for Cloudinary Ruby SDK
Before proceeding, please update to latest version and test if the issue persists

## Describe the bug in a sentence or two.
When uploading raw files (e.g. CSV) through the ActiveStorage integration, the Cloudinary API rejects the upload with CloudinaryException: An unknown file format not allowed.

This is a regression from the 1.x series, which used rest-client and preserved the original filename in multipart requests.

## Issue Type (Can be multiple)
- [ ] Build - Cannot install or import the SDK
- [ ] Performance - Performance issues
- [x] Behaviour - Functions are not working as expected (such as generate URL)
- [ ] Documentation - Inconsistency between the docs and behaviour
- [ ] Other (Specify)

## Steps to reproduce
1. Configure ActiveStorage with the Cloudinary service (config/storage.yml):
```
cloudinary:
service: Cloudinary
type: private
```

2. Configure a Cloudinary upload preset as the default for "API raw" with allowed_formats: ["csv"]
3. Create a model with has_one_attached :csv_file
4. Upload a .csv file through ActiveStorage
5. Observe the error:
```
ActiveStorage::IntegrityError (An unknown file format not allowed)
Caused by: CloudinaryException (An unknown file format not allowed)
```

## Error screenshots or Stack Trace (if applicable)
…

## Operating System
- [ ] Linux
- [ ] Windows
- [ ] macOS
- [x] All

## Environment and Libraries (fill in the version numbers)
- Cloudinary Ruby SDK version - 2.1.2
- Ruby Version - 3.4.1
- Rails Version - 8.1.2
- Other Libraries (Carrierwave, ActiveStorage, etc) - 0.0.0

## Repository

If possible, please provide a link to a reproducible repository that showcases the problem

## Suggested Fix
In `lib/active_storage/service/cloudinary_service.rb`, the upload method should pass the filename to the uploader as original_filename:

```ruby
def upload(key, io, filename: nil, checksum: nil, **options)
instrument :upload, key: key, checksum: checksum do
begin
extra_headers = checksum.nil? ? {} : {Headers::CONTENT_MD5 => checksum}
options = @options.merge(options)
options[:original_filename] = filename.to_s if filename.present? # <-- add this
resource_type = resource_type(io, key)
options[:format] = ext_for_file(key) if resource_type == "raw"
Cloudinary::Uploader.upload_large(
io,
# ... rest unchanged
)
end
end
end
```