Add parsing helper functions for DateTime, Date, Time, and Duration

[sudoscrawl]

Pull Request Check List

• Added tests for changed code.
• Updated documentation for changed code.

This PR adds parsing helper functions:

• parse_datetime
• parse_date
• parse_time
• parse_duration

These functions provide a convenient to parse string without having to use assert isinstance(..., Time) etc. everytime while parsing in type checked codebases.
Closes #917

[codspeed-hq]

Merging this PR will not alter performance

✅ 1 untouched benchmark

---

_{Comparing sudoscrawl:master (dfda184) with master (0a88aec)}