Function calculate_remaining_lockout_minutes 

pub fn calculate_remaining_lockout_minutes(
    last_timestamp: &SystemTime,
    lockout_duration_minutes: u32,
) -> Option<u32>

What: Calculate remaining lockout time in minutes based on last failed attempt timestamp.

Inputs:

• last_timestamp: Timestamp of the last failed attempt.
• lockout_duration_minutes: Total lockout duration in minutes.

Output:

• Some(minutes) if still locked out, None if lockout has expired.

Details:

• Calculates time elapsed since last failed attempt.
• Returns remaining minutes if lockout is still active, None if expired.