Improve DT Modifier coverage

[FletcherDares]

No description provided.

[github-actions]

AI review done up to commit: 7d34c12

AI Review Summary:

The changes introduce new test cases to the test_parse_modifier_error_cases function in src/db/table/operations/helpers/datetime_functions/modifiers.rs. These tests cover a comprehensive set of invalid date, time, and modifier string inputs, including leap year checks and out-of-range values. The overall quality of the changes is good, as they improve the test coverage and robustness of the parse_modifier function by explicitly testing various error conditions. No specific issues or patterns of errors were observed.