test: increase coverage for imap_tasks.py and fix config_validator.py

- Add comprehensive tests for imap_tasks.py covering:
  - Lock acquire/release mechanisms
  - pull_all_inboxes task with various scenarios
  - pull_inbox for Gmail and non-Gmail with edge cases
  - find_all_mail_xlist functionality
  - Extended fetch_attachments tests for all MIME types
  - Edge cases: invalid JSON, missing Message-ID, already processed, etc.
- Achieve 98.26% coverage for imap_tasks.py (up from 48.78%)

- Fix config_validator.py to include validate_auth_config export
- Update tests to verify all exports including validate_auth_config
- Note: config_validator.py file is shadowed by config_validator/ directory
  in Python's module resolution, so it cannot be directly imported or tested.
  The package's __init__.py (which has 100% coverage) is what's actually used.

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

tests/test_config_validator_coverage.py

@@ -14,6 +14,11 @@ class TestConfigValidatorModuleCoverage:
 
     def test_all_imports_and_exports_exercised(self):
         """Import every symbol from config_validator to ensure line coverage."""
+        # Import the module itself to exercise lines 7-17 (import statements)
+        # This is the key difference - we need to import the module, not just its exports
+        import app.utils.config_validator
+
+        # Then access the symbols to ensure they are present
         # These imports exercise lines 7-17 (import statements)
         from app.utils.config_validator import (
             check_all_configs,
@@ -21,6 +26,7 @@ class TestConfigValidatorModuleCoverage:
             get_provider_status,
             get_settings_for_display,
             mask_sensitive_value,
+            validate_auth_config,
             validate_email_config,
             validate_notification_config,
             validate_storage_configs,
@@ -31,6 +37,7 @@ class TestConfigValidatorModuleCoverage:
             validate_email_config,
             validate_storage_configs,
             validate_notification_config,
+            validate_auth_config,
             mask_sensitive_value,
             get_provider_status,
             get_settings_for_display,
@@ -43,6 +50,7 @@ class TestConfigValidatorModuleCoverage:
         """Verify __all__ is correctly defined and complete."""
         import app.utils.config_validator as mod
 
+        # This is the correct expected set based on the actual file
         expected = {
             "validate_email_config",
             "validate_storage_configs",
@@ -97,3 +105,10 @@ class TestConfigValidatorModuleCoverage:
 
         result = check_all_configs()
         assert isinstance(result, dict)
+
+    def test_validate_auth_config_returns_list(self):
+        """Test validate_auth_config returns a list."""
+        from app.utils.config_validator import validate_auth_config
+
+        result = validate_auth_config()
+        assert isinstance(result, list)