v0.2.0

Breaking changes

• SerdesBase → PaperJsonBase — inherit from PaperJsonBase for type-safe to_json() / from_json().
• SerdesProtocol → PaperJsonProtocol — use in type annotations for structural typing.
• Removed .pyi type stub files.

Docs & DX

• Added Overview section to the README explaining automatic type stringification (the round-trip str() fallback).
• Updated docstrings across the codebase to reflect the new class names.

Infrastructure

• Bumped CI workflow actions: actions/checkout@v4 → v6, astral-sh/setup-uv@v5 → v8.1.0.