Fix: PATCH endpoint replacing resources instead of adding them

[rbardaji]

PATCH /dataset/{id} was replacing all existing resources instead of adding new ones, making it behave identically to PUT.

Before: PATCH replaced all resources (incorrect)
After: PATCH adds new resources to existing ones (correct)

Fixes #92

Changes

• Modified patch_general_dataset() in api/services/dataset_services/general_dataset.py
• Resources are now merged instead of replaced during PATCH operations
• Existing resources are preserved and new ones are added
• PUT behavior unchanged (still replaces all resources)

Testing

Reproduction Test Results

# Before fix
Initial resources: 1 → Final resources: 1 ❌ (replaced)

# After fix  
Initial resources: 1 → Final resources: 2 ✅ (added)

Verification

• PATCH adds resources without removing existing ones
• PATCH updates existing resources by URL/name matching
• PUT behavior unchanged
• No regression in other dataset fields
• Manual API testing completed

API Behavior

PATCH /dataset/{id} (Fixed)

{
  "resources": [{"url": "new.json", "name": "new_resource"}]
}

Result: Adds to existing resources ✅

PUT /dataset/{id} (Unchanged)

{
  "resources": [{"url": "replacement.csv", "name": "replacement"}]
}

Result: Replaces all resources ✅

Review Checklist

• Reproduction script confirms bug existed
• Fix verified with enhanced test script
• No breaking changes (fixes incorrect behavior)
• Maintains backward compatibility
• Code follows existing conventions