fix(req): ignore trailing root dot in subdomains

[lin-hongkuan]

This strips an optional trailing DNS root dot before calculating req.subdomains, so fully qualified hostnames behave like their ordinary hostname form.

The regression test covers tobi.ferrets.example.com. and keeps existing subdomain offset behavior unchanged.

Validation:

• npx mocha --require test/support/env --check-leaks test/req.subdomains.js
• npm run lint
• git diff --check

AI-assisted: Codex helped prepare this focused change; I reviewed the diff and ran the validation above before submitting.

[krzysdz]

Everyone loves trailing dots.

For anyone looking into this:

tobi.ferrets.example.com. is a valid way to specify FQDN that is usually written as tobi.ferrets.example.com. The usual version without trailing dot, can technically be treated as a subdomain of some local domain in some cases. This being said, everyone expects the version without . and sometimes it is hard to decide what to do when someone specifies a host with a trailing dot.

In this case I'd say that req.subdomains given either tobi.ferrets.example.com or tobi.ferrets.example.com. should return ['ferrets', 'tobi']. Currently if the trailing dot is present it returns ['example', 'ferrets', 'tobi'].

[krzysdz]

A regular expression is going to be slower than something like:

Suggested change

	hostname = hostname.replace(/\.$/, '');
	if (hostname[hostname.length - 1] === '.') {
	hostname = hostname.slice(0, -1);
	}