Testing defaults against NumPy's functions

[joaosferreira]

Testing multimethods' default implementations against the corresponding NumPy functions and comparing their results allows for a better development by identifying and potentially covering more corner cases, resulting in robust and accurate implementations.
The default implementation for the norm function in the Linear Algebra module should serve as a good starting point for putting this into practice as it has enough of these cases. Most of norm_default is already implemented in 366057b.

This was briefly mentioned in #56 (comment) and further discussed here.