Defines common mathematical constants as double values:
e – Euler’s number (base of natural logarithms). Approximately 2.718281828459045.pi – Ratio of a circle’s circumference to its diameter. Approximately 3.141592653589793.phi – The golden ratio (1 + sqrt(5)) / 2. Approximately 1.618033988749895.These constants are used throughout the math modules. They mirror the definitions in Dart’s dart:math but are provided here for convenience and to avoid importing the full math library.