Adding whenever in date & time section

[KishanPipariya]

What are you adding?

• Project name: whenever
• GitHub URL: - https://github.com/ariebovenberg/whenever
• Category: Date & Time
• Description (one line): Typed and DST-safe datetimes for Python

Checklist

• The project is Python-related and has a meaningful Rust component
• The GitHub URL is correct and the project is actively maintained
• The entry follows the format: [name](url) - Description.
• The description starts with a capital letter and ends with a period
• The project is placed in the correct category
• No duplicate entry exists in the list

[ritwiktiwari]

Thanks for adding whenever.
Would it be possible for you to add libraries listed in #7?