Feat: Add tests and refactor UserBan model functionality

UserBan Model
- Added new functionality:
- Automatically bans a user permanently if no start or end date is provided, and marks this in the admin interface as a permanent ban.
- Allowed banning from a specific start date to an end date.
- Enabled banning a user for a specific number of days.
- Implemented signals:
- Automatically unbans a user when their BanUser record is deleted.
Admin Interface
- Added form validation to prevent banning a user twice.
- Made start and end dates optional for permanent bans.
- Raised an error if only a start or end date is provided without the other.
- If no dates are available because it is a permanent ban an N/A is shown for both dates
Helper Functions (for testing)
- create_permanently_banned_user: Creates a permanently banned user.
- create_temporarily_banned_user: Creates a temp-banned user with a date range.
- create_banned_user_for_days: Bans a user for a specific number of days.
Added methods in the utils
- current_time: Returns the current datetime
- is_date_valid: Checks if a date is a datetime object.
Testing Enhancements
- Modified start date and end date tests to ignore microseconds and seconds for consistency in comparison, ensuring tests no longer fail due to slight timing differences.
- Added a comprehensive set of tests, including coverage for the newly refactored ban method.

EgbieAndersonUku1 / Fullstack-fruit-and-veg