feat: Add Python SDK with async/await support and comprehensive Telecom Platform API integration

- Add TelecomSDK class with async context manager and aiohttp ClientSession with 30s timeout, 3 retries
- Add subscriber management: get_subscriber, list_subscribers with pagination/status filter, create_subscriber, update_subscriber, suspend_subscriber, activate_subscriber, terminate_subscriber
- Add usage tracking: get_usage_stats with date range, list_usage_events with filtering, get_real_time_usage

sdk/python/telecom_sdk/exceptions.py

@@ -0,0 +1,31 @@
+class TelecomError(Exception):
+    """Base exception for all Telecom SDK errors."""
+    
+    def __init__(self, message: str, status_code: Optional[int] = None, response_data: Optional[dict] = None):
+        super().__init__(message)
+        self.status_code = status_code
+        self.response_data = response_data or {}
+
+
+class AuthenticationError(TelecomError):
+    pass
+
+
+class APIError(TelecomError):
+    pass
+
+
+class NetworkError(TelecomError):
+    pass
+
+
+class ValidationError(TelecomError):
+    pass
+
+
+class RateLimitError(TelecomError):
+    pass
+
+
+class ServerError(TelecomError):
+    pass