Add stubs file for constants

src/scipy-stubs/constants.pyi

+#!/usr/bin/env python3
+"""
+Stub file for sciypy-constants.
+"""
+pi: float
+golden: float
+golden_ratio: float
+N_A: float
+Avogadro: float
+Boltzmann: float
+gas_constant: float
+
+
+value(key: str) -> float: ...
+
+
+unit(key: str) -> str: ...
+
+
+precision(key: str) -> float: ...
+
+
+physical_constants: dict[str, tuple[float, str, float]]