[CHA-1656] Support Campaign

[rafaelmf3]

Add Campaign Feature Support to Ruby SDK

Summary

This PR adds complete campaign feature support to the stream-chat-ruby SDK, matching the Python SDK implementation. All 7 backend campaign routes are now fully implemented and tested.

Backend Routes Implemented

• ✅ POST /campaigns - Create campaign
• ✅ GET /campaigns/{id} - Get campaign by ID
• ✅ PUT /campaigns/{id} - Update campaign
• ✅ DELETE /campaigns/{id} - Delete campaign
• ✅ POST /campaigns/{id}/start - Start campaign (with optional scheduling)
• ✅ POST /campaigns/{id}/stop - Stop campaign
• ✅ POST /campaigns/query - Query campaigns with filters and sorting

Changes

New Files

• lib/stream-chat/campaign.rb - Campaign class following the Channel class pattern
  • Methods: create, get, update, delete, start, stop
  • Proper error handling and data merging

Modified Files

• lib/stream-chat/client.rb
  • Added campaign() factory method
  • Added 7 campaign methods matching all backend routes
  • Proper datetime handling using normalize_timestamp
  • Added require for campaign class

Test Files

• spec/campaign_spec.rb - Comprehensive RSpec tests covering:
  • Campaign CRUD operations
  • Start/stop with scheduling
  • Query campaigns with filters
  • Direct client method usage

Features

• Campaign Class: Object-oriented interface similar to Channel class
• Factory Method: client.campaign() for easy campaign instance creation
• Direct Client Methods: All operations available directly on client
• DateTime Support: Automatic conversion for scheduled_for and stop_at parameters
• Query Support: Full filter conditions, sorting, and pagination
• Type Safety: All methods have Sorbet type signatures
• Error Handling: Proper exception handling with StreamChannelException

Code Quality

• ✅ All code passes Rubocop linting
• ✅ All methods have Sorbet type signatures
• ✅ Follows existing SDK patterns (Channel class pattern)
• ✅ Ruby 3.0, 3.1, and 3.4 compatible
• ✅ Comprehensive unit tests with proper cleanup

Testing

All campaign tests pass successfully:

• Campaign creation (with and without ID)
• Full CRUD operations
• Start/stop with scheduling
• Query campaigns
• Direct client method usage

Example Usage

Using Campaign class

campaign = client.campaign(
  data: {
    message_template: { text: 'Hello' },
    sender_id: 'user-1',
    user_ids: ['user-2'],
    name: 'My Campaign'
  }
)
created = campaign.create
campaign.get
campaign.update(name: 'Updated Name')
campaign.start(scheduled_for: Time.now + 3600)
campaign.stop
campaign.delete

Using direct client methods

client.create_campaign(data: {...})
client.get_campaign(campaign_id)
client.update_campaign(campaign_id, data)
client.start_campaign(campaign_id, scheduled_for: time)
client.stop_campaign(campaign_id)
client.delete_campaign(campaign_id)
client.query_campaigns(filter_conditions, sort: {...})

CLA

• I have signed the Stream CLA (required).
• The code changes follow best practices
• Code changes are tested (add some information if not applicable)

Description of the pull request