Implement a new optional Math module for the Wren standard library, gated behind the WREN_USE_LIB_MATH flag (default on). The module provides double-precision math functions (abs, ceil, floor, int, frac, sin, cos, tan, deg, rad) and a xorshift-based pseudo-random number generator with srand/rand methods. Includes comprehensive test files for each function and an all_tests runner.
