[Request] Host fallback paths do not normalize malformed SERVER_NAME values with an embedded port

[RedZapdos123]

Description:

When HTTP_HOST is missing and SERVER_NAME already contains :port, Rage does not normalize the fallback host value before using it in request-host code paths.

This is an edge case Rack env, but it currently breaks multiple host-based paths on latest main.

MRE:

require "domain_name"
require "./lib/rage/all"

request_env = {
  "REQUEST_METHOD" => "GET",
  "rack.url_scheme" => "http",
  "PATH_INFO" => "/",
  "QUERY_STRING" => "",
  "rack.input" => StringIO.new,
  "SERVER_NAME" => "google.com:3000",
  "SERVER_PORT" => "3000"
}

request = Rage::Request.new(request_env)
puts "request.host => #{request.host.inspect}"
puts "request.url => #{request.url.inspect}"
puts "request.domain => #{request.domain.inspect}"

router = Rage::Router::Backend.new
router.on("GET", "/photos", ->(_) { "get photos" }, constraints: { host: "google.com" })
route_env = request_env.merge("PATH_INFO" => "/photos")
handler = router.lookup(route_env)
puts "router.lookup => #{handler.inspect}"

cookie_env = request_env.merge("SERVER_NAME" => "cookie.test.com:3000")
headers = {}

begin
  cookies = Rage::Cookies.new(cookie_env, headers)
  cookies[:x] = { value: 1, domain: :all }
  puts "cookies header => #{headers.inspect}"
rescue => e
  puts "cookies error => #{e.class}: #{e.message}"
end

Current behavior:

• request.host is nil.
• request.url becomes "http://google.com:3000:3000/".
• request.domain is nil.
• exact host constraints do not match because router.lookup returns nil.
• cookie domain resolution can raise TypeError: NilClass is not a String when domain: :all is used.

Actual output:

request.host => nil
request.url => "http://google.com:3000:3000/"
request.domain => nil
router.lookup => nil
cookies error => TypeError: NilClass is not a String

Expected behavior:

• Rage should normalize the fallback host the same way it normalizes HTTP_HOST, even if SERVER_NAME is malformed and already includes a port.
• request.host should be "google.com".
• request.url should be "http://google.com:3000/".
• request.domain should be "google.com".
• exact host constraints for "google.com" should still match.
• cookie domain resolution should derive from "cookie.test.com" instead of raising.