[Task] Update docstrings for the public API

[Apricot-S]

Summary

Create a checklist of all public API elements and update their docstrings according to the style chosen in #120.

Scope

• Choose a unified docstring style for the project
  • Candidates: Google, NumPy, reST
  • Note: some existing docstrings already use reST
• Set [tool.ruff.lint.pydocstyle]
• List all public constants, classes, functions, and methods
• Create a checklist for tracking docstring updates
• Update docstrings to follow the unified style

Public API checklist

• __init__.py
  • (none)
• agari.py
  • Agari.is_agari()
• (TODO)