URI Validation Performance Improvements
URI Validation Performance Improvements

I've found _is_valid_uri to be a hotspot in serialization and
deserialization.

Benchmarking this version of the function against the original with 1e7
urls results in runtime improvement of ~2x.

Tests against real RDF graphs with 2e6+ triples results in runtime
improvement of ~8% in serialization and deserialization.

RDFLib/rdflib,RDFLib/rdflib,RDFLib/rdflib,RDFLib/rdflib