Add Download Control Functionality (Pause/Resume/Cancel) Issue#53

[Kcodess2807]

📋 Summary
This PR adds comprehensive download control functionality to the GitHubDownloader Python API, enabling users to pause, resume, and cancel active downloads. This provides better control over long-running download operations and improves the overall user experience.

🔗 Related Issue
Closes #53 - Add download control functionality

🚀 Changes Made
✨ New Features

• cancel_current_download() - Cancel active downloads immediately
• Returns DownloadResult with CANCELLED status
• Returns None if no active download
• pause_current_download() - Pause active downloads
• Async method that pauses current operation
• Returns DownloadResult with PAUSED status
• Returns None if no active download
• resume_current_download() - Resume paused downloads
• Async method that resumes paused operation
• Returns DownloadResult with IN_PROGRESS status
• Returns None if no paused download
• 🔧 Technical Implementation
• Leverages existing orchestrator control methods
• Maintains thread-safe operations
• Proper async/await patterns for pause/resume
• Synchronous cancel for immediate termination

📝 Usage Examples
Basic Control Operations

from forklet import GitHubDownloader

downloader = GitHubDownloader()

# Start a download (in background)
download_task = asyncio.create_task(
    downloader.download("large-org", "huge-repo", "./downloads")
)

# Pause the download
result = await downloader.pause_current_download()
if result:
    print(f"Download paused: {result.status}")

# Resume the download
result = await downloader.resume_current_download()
if result:
    print(f"Download resumed: {result.status}")

# Cancel the download
result = downloader.cancel_current_download()
if result:
    print(f"Download cancelled: {result.status}")

Complete Workflow

# Workflow: start -> pause -> resume -> cancel
async def controlled_download():
    downloader = GitHubDownloader()
    
    # Start download in background
    download_task = asyncio.create_task(
        downloader.download("tensorflow", "tensorflow", "./tf")
    )
    
    # Wait a bit, then pause
    await asyncio.sleep(5)
    await downloader.pause_current_download()
    
    # Wait, then resume
    await asyncio.sleep(2)
    await downloader.resume_current_download()
    
    # Wait, then cancel
    await asyncio.sleep(5)
    downloader.cancel_current_download()

🧪 Testing
Test Coverage
✅ 11 comprehensive tests covering all control scenarios
✅ Success and edge cases for each operation
✅ Complete workflow testing (pause -> resume -> cancel)
✅ Async operation testing with proper mocking

[Einswilli]

Simple and clean!
Thanks!