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/streaming/Provider.py

@@ -1,7 +1,24 @@
 from abc import ABC, abstractmethod
+from typing import Any
 
 
 class Provider(ABC):
+    """Abstract base class for streaming providers."""
+
     @abstractmethod
-    def GetLink(self, embededLink: str, DEFAULT_REQUEST_TIMEOUT: int) -> (str, [str]):
-        pass
+    def get_link(
+        self, embedded_link: str, timeout: int
+    ) -> tuple[str, dict[str, Any]]:
+        """
+        Extract direct download link from embedded player link.
+
+        Args:
+            embedded_link: URL of the embedded player
+            timeout: Request timeout in seconds
+
+        Returns:
+            Tuple of (direct_link: str, headers: dict)
+                - direct_link: Direct URL to download resource
+                - headers: Dictionary of HTTP headers to use for download
+        """
+