Add account deletion scheduler and comprehensive tests

- Implemented account deletion scheduler in `account_deletion_scheduler.py` to manage user deletions based on a defined threshold.
- Added logging for deletion processes, including success and error messages.
- Created tests for deletion logic, including edge cases, retry logic, and integration tests to ensure complete deletion workflows.
- Ensured that deletion attempts are tracked and that users are marked for manual intervention after exceeding maximum attempts.
- Implemented functionality to check for interrupted deletions on application startup and retry them.

backend/config/deletion_config.py

@@ -0,0 +1,61 @@
+import os
+import logging
+
+logger = logging.getLogger(__name__)
+
+# Account deletion threshold in hours
+# Default: 720 hours (30 days)
+# Minimum: 24 hours (1 day)
+# Maximum: 720 hours (30 days)
+
+try:
+    ACCOUNT_DELETION_THRESHOLD_HOURS = int(os.getenv('ACCOUNT_DELETION_THRESHOLD_HOURS', '720'))
+except ValueError as e:
+    raise ValueError(
+        f"ACCOUNT_DELETION_THRESHOLD_HOURS must be a valid integer. "
+        f"Invalid value: {os.getenv('ACCOUNT_DELETION_THRESHOLD_HOURS')}"
+    ) from e
+
+# Validation
+MIN_THRESHOLD_HOURS = 24
+MAX_THRESHOLD_HOURS = 720
+
+def validate_threshold(threshold_hours=None):
+    """
+    Validate the account deletion threshold.
+    
+    Args:
+        threshold_hours: Optional threshold value to validate. If None, validates the module's global value.
+        
+    Returns True if valid, raises ValueError if invalid.
+    """
+    value = threshold_hours if threshold_hours is not None else ACCOUNT_DELETION_THRESHOLD_HOURS
+    
+    if value < MIN_THRESHOLD_HOURS:
+        raise ValueError(
+            f"ACCOUNT_DELETION_THRESHOLD_HOURS must be at least {MIN_THRESHOLD_HOURS} hours. "
+            f"Current value: {value}"
+        )
+    
+    if value > MAX_THRESHOLD_HOURS:
+        raise ValueError(
+            f"ACCOUNT_DELETION_THRESHOLD_HOURS must be at most {MAX_THRESHOLD_HOURS} hours. "
+            f"Current value: {value}"
+        )
+    
+    # Warn if threshold is less than 7 days (168 hours)
+    if value < 168:
+        logger.warning(
+            f"Account deletion threshold is set to {value} hours, "
+            "which is below the recommended minimum of 7 days (168 hours). "
+            "Users will have limited time to recover their accounts."
+        )
+    
+    if threshold_hours is None:
+        # Only log this when validating the module's global value
+        logger.info(f"Account deletion threshold: {ACCOUNT_DELETION_THRESHOLD_HOURS} hours")
+    
+    return True
+
+# Validate on module import
+validate_threshold()