refactor: improve code quality - fix imports, type hints, and security issues

## Critical Fixes
- Create error_handler module with custom exceptions and recovery strategies
  - Adds RetryableError, NonRetryableError, NetworkError, DownloadError
  - Implements with_error_recovery decorator for automatic retry logic
  - Provides RecoveryStrategies and FileCorruptionDetector classes
  - Fixes critical import error in enhanced_provider.py

- Fix CORS security vulnerability in fastapi_app.py
  - Replace allow_origins=['*'] with environment-based config
  - Use settings.cors_origins for production configurability
  - Add security warnings in code comments

## Type Hints Improvements
- Fix invalid type hint syntax in Provider.py
  - Change (str, [str]) to tuple[str, dict[str, Any]]
  - Rename GetLink() to get_link() (PEP8 compliance)
  - Add comprehensive docstrings for abstract method

- Update streaming provider implementations
  - voe.py: Add full type hints, update method signature
  - doodstream.py: Add full type hints, update method signature
  - Fix parameter naming (embededLink -> embedded_link)
  - Both now return tuple with headers dict

- Enhance base_provider.py documentation
  - Add comprehensive type hints to all abstract methods
  - Add detailed parameter documentation
  - Add return type documentation with examples

## Files Modified
- Created: src/core/error_handler.py (error handling infrastructure)
- Modified: 9 source files (type hints, naming, imports)
- Added: QUALITY_IMPROVEMENTS.md (implementation details)
- Added: TEST_VERIFICATION_REPORT.md (test status)
- Updated: QualityTODO.md (progress tracking)

## Testing
- All tests passing (unit, integration, API)
- No regressions detected
- All 10+ type checking violations resolved
- Code follows PEP8 and PEP257 standards

## Quality Metrics
- Import errors: 1 -> 0
- CORS security: High Risk -> Resolved
- Type hint errors: 12+ -> 0
- Abstract method docs: Minimal -> Comprehensive
- Test coverage: Maintained with no regressions

src/core/providers/enhanced_provider.py

@@ -18,7 +18,12 @@ from urllib.parse import quote
 
 import requests
 from bs4 import BeautifulSoup
-from error_handler import (
+from fake_useragent import UserAgent
+from requests.adapters import HTTPAdapter
+from urllib3.util.retry import Retry
+from yt_dlp import YoutubeDL
+
+from ..error_handler import (
     DownloadError,
     NetworkError,
     NonRetryableError,
@@ -27,11 +32,6 @@ from error_handler import (
     recovery_strategies,
     with_error_recovery,
 )
-from fake_useragent import UserAgent
-from requests.adapters import HTTPAdapter
-from urllib3.util.retry import Retry
-from yt_dlp import YoutubeDL
-
 from ..interfaces.providers import Providers
 from .base_provider import Loader
 
@@ -792,7 +792,7 @@ class EnhancedAniWorldLoader(Loader):
             if not provider:
                 raise NonRetryableError("VOE provider not available")
 
-            return provider.GetLink(
+            return provider.get_link(
                 embedded_link, self.DEFAULT_REQUEST_TIMEOUT
             )