typing: add type hints to parser helper functions (#938)

[DaBestCode]

Linked issue

• Contributes to Add type hints [beginner, Python, typing] #938

Description

This pull request adds comprehensive type hints to parser helper functions in the icalendar library, contributing to issue #938's goal of adding type hints throughout the codebase.

Changes Made

1. src/icalendar/parser_tools.py:

   • Enhanced to_unicode() docstring with a "Returns" section to better document the function's return behavior

2. src/icalendar/parser/parameter.py:

   • Added return type annotation -> Callable to the single_string_parameter() decorator function
   • Added parameter type annotation upper: bool = False to clarify the upper parameter's type
   • Added return type hints to inner functions:
     • decorator(): -> property
     • fget(): -> str | None (getter returns optional string)
     • fset(): -> None (setter returns None)
     • fdel(): -> None (deleter returns None)

3. news/938.chore.2:

   • Added changelog entry documenting the type hint improvements

Benefits

• Improved IDE autocompletion and type checking support
• Better documentation through explicit type hints
• Compatibility with static type checkers (mypy, pyright, etc.)
• No changes to runtime behavior or logic

Checklist

• I added a change log entry, following the instructions in all subsections under Change log requirements.
• I followed icalendar's Artificial intelligence policy and disclosed my Responsible AI use in my commit messages, if applicable.
• I ran and ensured all tests pass locally by following Run tests.

Additional information

• All existing tests pass (pytest src/icalendar/tests/test_unit_parser_tools.py and parameter-related tests)
• Type hints follow PEP 484 conventions using Python 3.10+ union syntax (|)
• Changes are backward compatible and contain no breaking changes

[github-actions]

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[github-actions]

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[read-the-docs-community]

Documentation build overview

📚 icalendar | 🛠️ Build #34305970 | 📁 Comparing f57bc6f against latest (59da8b8)

  🔍 Preview build  

4 files changed

± _modules/icalendar/parser_tools.html
± reference/api/icalendar.parser.parameter.html
± reference/api/icalendar.parser_tools.html
± _modules/icalendar/parser/parameter.html

[stevepiercy]

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