update signatures and annotations

[davidism]

• Use deferred evaluation of annotations (from __future__ import annotations).
• Implement str methods directly, instead of using wrapper functions. The primary reason was to make pyright understand the types for each method. But this should also result in some amount of speedup, since the wrapper does not need to run at import, and methods can escape their exact arguments directly rather than incurring two function calls and multiple isinstance checks.
• Use positional-only arguments, and refactor argument names. For str methods, this makes the signatures match those reported by python -m pydoc str. Also added to local functions and methods, such as escape(s, /), to better match the str signatures.
• Add type annotations to tests.
• Check types with pyright, both pyright and pyright --verifytypes pass.