src: various minor improvements to node_url

Went hunting for possible performance improvements. Didn't find
anything significant but did manage to make a number of style
improvements that bring more in line with style guidelines and
good pratice.

PR-URL: https://github.com/nodejs/node/pull/31651


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>