Making static::unitNameOfAliasesAlreadyRegistered optional depending on environment

[vasily-kartashov]

Can you think of the best way to make the uniqueness test in AbstractPhysicalQuantity::addUnit:24 optional? Profiling says this is by far the slowest part of the library. It's a great feature for development environment, but there's little reason to incur this penalty in production environment, especially with a proper CI set up.

Same applies for HasSIUnitsTrait::addMissingSIPrefixUnits:191.