[maintenance] Remove `pyrightconfig.json` and keep Pyright config in `pyproject.toml`

[MSM2002]

The project currently has both pyrightconfig.json and [tool.pyright] in pyproject.toml. When pyrightconfig.json exists, Pyright ignores the pyproject.toml configuration, which can lead to confusion and mismatched settings.

To avoid silent config conflicts and keep a single source of truth, we should delete pyrightconfig.json and keep the Pyright configuration in pyproject.toml.

This aligns with modern tooling conventions and simplifies maintenance.