test : added edge case tests for parse_to_utc in time_utils

[tmdeveloper007]

Closes #2422.

Summary of What Has Been Done:
Created a new test file testing/backend/unit/test_time_utils_parse_utc_edge_cases.py with 11 edge case tests for parse_to_utc() in backend/secuscan/time_utils.py.

The existing test_time_utils.py covers happy-path ISO 8601 formats only. This file adds tests for malformed inputs, None, empty strings, non-string types, and the 'now' literal.

Changes Made:

• New file: testing/backend/unit/test_time_utils_parse_utc_edge_cases.py
• Added TestParseToUtcEdgeCases class with 11 tests covering:
  • None input returns None
  • Empty string returns None
  • Whitespace-only string returns None
  • Garbage strings ("not-a-date", "hello world") return None
  • Integer Unix timestamps return UTC datetime
  • Float Unix timestamps return UTC datetime
  • 'now' literal returns current UTC time
  • List input converted to string and returns None
  • Boolean True treated as Unix timestamp (epoch + 1 second)
  • Boolean False treated as Unix timestamp (epoch)

Impact it Made:

• Ensures parse_to_utc degrades gracefully on malformed input rather than raising unhandled exceptions
• Prevents crashes when scan data contains garbage timestamps
• Documents the behavior of non-string type inputs

Note: This task is being handled by tmdeveloper007 — please assign to that account when picking it up.

[utksh1]

Closing this PR as a duplicate of #2327, which is the earlier and broader submission for the same helper/test surface. Please continue any fixes in #2327 so the repository does not merge duplicate test files or split the coverage across competing PRs.