Fix compatibility issue with URL attachments wrong number of arguments (crmne#250)

- Fix ArgumentError: wrong number of arguments (given 2, expected 0..1)
that occurs when Marcel processes URI objects
- Use filename-based MIME detection for URLs instead of passing URI
objects to Marcel
- Add test that reproduces the issue and validates the fix
- Maintains backward compatibility and improves performance by avoiding
network calls

<img width="1316" alt="Screenshot 2025-06-16 at 9 34 13 AM"
src="https://github.com/user-attachments/assets/b0d29eeb-66aa-45b5-aed9-5c33adf0c0b7"
/>

## What this does

<!-- Clear description of what this PR does and why -->

## Type of change

- [x] Bug fix
- [ ] New feature
- [ ] Breaking change
- [ ] Documentation
- [ ] Performance improvement

## Scope check

- [x] I read the [Contributing
Guide](https://github.com/crmne/ruby_llm/blob/main/CONTRIBUTING.md)
- [x] This aligns with RubyLLM's focus on **LLM communication**
- [x] This isn't application-specific logic that belongs in user code
- [x] This benefits most users, not just my specific use case

## Quality check

- [x] I ran `overcommit --install` and all hooks pass
- [x] I tested my changes thoroughly
- [ ] I updated documentation if needed
- [x] I didn't modify auto-generated files manually (`models.json`,
`aliases.json`)

## API changes

- [ ] Breaking change
- [ ] New public methods/classes
- [ ] Changed method signatures
- [x] No API changes

## Related issues

Fixes crmne#247

---------

Co-authored-by: Carmine Paolino <carmine@paolino.me>

Author: DustinFisher

lib/ruby_llm/attachment.rb

@@ -99,7 +99,7 @@ def to_h
     def determine_mime_type
       return @mime_type = active_storage_content_type if active_storage? && active_storage_content_type.present?
 
-      @mime_type = RubyLLM::MimeType.for(@source, name: @filename)
+      @mime_type = RubyLLM::MimeType.for(url? ? nil : @source, name: @filename)
       @mime_type = RubyLLM::MimeType.for(content) if @mime_type == 'application/octet-stream'
       @mime_type = 'audio/wav' if @mime_type == 'audio/x-wav' # Normalize WAV type
     end

spec/ruby_llm/chat_content_spec.rb

@@ -156,4 +156,30 @@
       end
     end
   end
+
+  describe 'URL attachment handling' do # rubocop:disable RSpec/MultipleMemoizedHelpers
+    it 'handles URL MIME type detection without ArgumentError' do
+      attachment = RubyLLM::Attachment.new(image_url)
+
+      expect(attachment.mime_type).to be_present
+    end
+
+    it 'creates content with URL attachments' do # rubocop:disable RSpec/MultipleExpectations
+      content = RubyLLM::Content.new('Describe this image', image_url)
+
+      expect(content.attachments).not_to be_empty
+      expect(content.attachments.first).to be_a(RubyLLM::Attachment)
+    end
+
+    it 'prevents ArgumentError: wrong number of arguments when processing URL attachments' do # rubocop:disable RSpec/MultipleExpectations
+      require 'open-uri' # required to trigger the marcel/open-uri compatibility issue
+
+      attachment = RubyLLM::Attachment.new(image_url)
+
+      expect { attachment.mime_type }.not_to raise_error
+
+      expect(attachment.mime_type).to eq('image/png')
+      expect(attachment.send(:url?)).to be true
+    end
+  end
 end