Validate byte-array-based namespaces passed into v3/5

[ctavan]

That byte-array-based namespaces aren't validated but string ones are is an inconsistency that should probably get addressed at some point so... yeah... @afterthought probably shouldn't count on this continuing to work in the future. But I don't see a compelling reason to close that particular loophole at the moment.

The alternative - adding an option to allow non-standard namespaces - flies in the face of the "this module adheres to the RFC" philosophy, so I'm a bit reticent to go that route.

'Kind of feels like we have a passable solution for the moment so maybe we can get away with looking the other way on this one until there's a reason to do otherwise. 🤷

Originally posted by @broofa in #511 (comment)

[josh-manton]

Is the above correct? It looks like it is reversed. string based uuids are getting passed to parse, while byte-array based name spaces by-pass parse and hence validate. The behavior should be the same, but I do believe that there should be a way to pass which validator you'd like, 'strict' which is fully RFC compliant, and 'lax' which only check the overall format of the string.

[broofa]

Closing until there's a reason to reopen.