fix: datetime verification evaluation about UTC in issuance and expiration

[peppelinux]

This pull request improves the handling of date-only validity periods in the MsoIssuer class by introducing a new date parsing method and updating the signing logic to ensure correct interpretation of expiry dates. It also adds a new test to verify that validity intervals are correctly set when issuance and expiry are on the same day.

Date parsing and validity handling improvements:

• Added a new static method parse_date to MsoIssuer in issuer.py to parse date-only strings and, when appropriate, set the time to the end of the day for expiry dates.
• Updated the sign method in MsoIssuer to use the new parse_date method for both issuance and expiry dates, ensuring expiry is interpreted as the end of the day.

Testing enhancements:

• Added a new test test_mso_issuer_validity_same_day to verify that when issuance and expiry dates are the same, the validity interval includes the entire day and the validUntil time is set to 23:59:59.
• Added necessary imports for datetime and cbor2 in the test file.