docs: merge __init__/__new__ docstrings into class docstrings

[Solaris-star]

Moves all constructor documentation from __init__/__new__ methods into their class docstrings so Sphinx renders them correctly with autoclass_content = 'class'.

• 17 methods migrated across 14 files
• Added test_no_init_docstrings.py — fails if any __init__/__new__ carries a docstring
• 14085 existing tests pass

Closes #1620

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[github-actions]

This pull request did not pass quality checks and AI use is suspected. Please review Contribute and make any necessary amendments.

[read-the-docs-community]

Documentation build overview

📚 icalendar | 🛠️ Build #33867398 | 📁 Comparing adccc9b against latest (926bc02)

  🔍 Preview build  

45 files changed · ± 45 modified

± Modified

• 404.html
• genindex.html
• _modules/icalendar/alarms.html
• _modules/icalendar/caselessdict.html
• _modules/icalendar/error.html
• reference/api/icalendar.alarms.html
• reference/api/icalendar.cal.alarm.html
• reference/api/icalendar.cal.availability.html
• reference/api/icalendar.cal.available.html
• reference/api/icalendar.cal.calendar.html
• and 35 more...

[stevepiercy]

@Solaris-star there is already another PR open, which I'm currently reviewing. #1622

I'd much rather have people review open PRs than create another PR for the same issue.

[Solaris-star]

Understood — closing this in favour of #1622. I'll go review that PR instead. Thanks for the heads up!