forked from extern/nushell
* added math product: working initial impl * resolving merge conflicts * impl std::ops::Mul for Filesize * rebased with main; refactored product implementation * fixed error msg, added docs for math product
* added math product: working initial impl * resolving merge conflicts * impl std::ops::Mul for Filesize * rebased with main; refactored product implementation * fixed error msg, added docs for math product