feat: allow prefixed env vars

[lalewis1]

For label_predicates, description_predicates etc. this commit allows you
to set the values as prefixed values. for example

# .env
LABEL_PREDICATES='["schema:headline", "dcterms:title"]'

this should work for any of the default bound prefixes in rdflib

Warning

i had to change the test cases becuase this now considers "1" to be an invalid prefix
this may or may not be a breaking change actually, so please consider carefully.

[recalcitrantsupplant]

I'd prefer not to do this as it relies on us knowing what namespace the prefix is mapped to, in common cases this may be clear but even for say schema: is that referring to the http or https version of schema, and for anything less common where would the mapping be kept, and how would you guarantee the prefix:namespace mappings are 1:1.

I realise perhaps counter intuitively the prez settings use the RDFLib Namespaces so can be written in the prefixed form