refactor: update date handling and remove deprecated constants
- Replaced the usage of datetime.now() with a new now() function from sientia_do.temporal.constants for consistent timestamp handling across multiple files.
- Updated the date format from DEFAULT_DATE_FORMAT to DATETIME_FORMAT_MS_WITH_TZ in various activities to ensure uniformity in timestamp formatting.
- Removed the obsolete patterns.py file that contained the DEFAULT_DATE_FORMAT constant.
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