docs: merge __init__/__new__ docstrings into class docstrings - #1623

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: astral-sh/setup-uv@d0d8abe699bfb85fec6de9f7adb5ae17292296ff. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

No file matched to [/home/runner/work/icalendar/icalendar/**/*requirements*.txt,/home/runner/work/icalendar/icalendar/**/*requirements*.in,/home/runner/work/icalendar/icalendar/**/*constraints*.txt,/home/runner/work/icalendar/icalendar/**/*constraints*.in,/home/runner/work/icalendar/icalendar/**/pyproject.toml,/home/runner/work/icalendar/icalendar/**/uv.lock,/home/runner/work/icalendar/icalendar/**/*.py.lock]. The cache will never get invalidated. Make sure you have checked out the target repository and configured the cache-dependency-glob input correctly.