Initial implementation of date

[saimeunt]

📝 Initial implementation of datetime utility

This PR provides an implementation of a datetime utility library in Cairo heavily inspired by chrono.
Most of the functions needed to manipulate dates are implemented.

🛠️ Issue

• Closes [FEAT]: Add DateTime Utility Implementation #165

📖 Description

Please refer to the chrono docs for usage as this utility aims at being a port of this rust library to Cairo.

Here's an example highlighting the basic operations available on datetimes, such as creating a DateTime from a starknet timestamp, simple formatting of dates and comparison.

#[test]
fn test_datetime_from_timestamp() {
    let dt1 = DateTimeTrait::from_timestamp(get_block_timestamp().try_into().unwrap()).unwrap();
    assert_eq!(format!("{}", dt1), "1970-01-01 00:00:00");
    start_cheat_block_timestamp_global(1707868800);
    let dt2 = DateTimeTrait::from_timestamp(get_block_timestamp().try_into().unwrap()).unwrap();
    assert_eq!(format!("{}", dt2), "2024-02-14 00:00:00");
    assert!(dt1 < dt2);
}

📝 Additional Notes

This utility being a port of chrono in Cairo, it is easy to cherry-pick missing functions from chrono that should be included in the Cairo version.