Adds `log` method to Num class via DEF_NUM_FN macro, and `pow(_)` method via a new DEF_PRIMITIVE that calls C's `pow()`. Registers both primitives in wrenInitializeCore. Includes new test files `test/core/number/log.wren` and `test/core/number/pow.wren` covering basic cases and edge values (negative input for log, zero exponent for pow). Also adds Sven Bergström to AUTHORS.