Fix computer.calendar dates issue

[supersational]

This is an excellent project!

Describe the changes you have made:

• Fix bug in coercing string from python datetime into applescript (this is localisation dependant so updated to use a function)
• Fix system messages which previously used end instead of end_date

Reference any relevant issues (e.g. "Fixes #000"):

Fixes #1148

Pre-Submission Checklist (optional but appreciated):

• [ ] I have included relevant documentation updates (stored in /docs)
• [x] I have read docs/CONTRIBUTING.md
• [x] I have read docs/ROADMAP.md

OS Tests (optional but appreciated):

• [ ] Tested on Windows
• [x] Tested on MacOS
• [ ] Tested on Linux

[KillianLucas]

Thank you so much for the kind words @supersational!! And great catch on computer.calendar, this is huge— I noticed that hallucination frequently but didn't spot these issues. Merging!

[theashworld]

Damn, it's 2024 and we are still struggling with dates and formatting. lol.

Thanks for the fix!