- add a { base: :show } quantization option to enable the behaviour
- align http.url with tag naming RFC (and Rack's #url) to include the
  complete request URL
- drop http.base_url when not unneeded
- preserve REQUEST_URI logic that differs from Rack's logic
- add SCRIPT_NAME which was previously unhandled for PATH_INFO
- append QUERY_STRING when using PATH_INFO to match REQUEST_URI

Note: there seems to be leakage between spec cases, which made this test
case flaky, with quantization option being set to show foo (example
seed: 63620). The test case was previously unaffected by this leakage
because it could not handle query strings.

Rack http.url tag now properly takes SCRIPT_NAME into account in the
PATH_INFO case, consistently with REQUEST_URI. These expectations did
not account for that.

- restore the previous default behaviour of `Quantization::HTTP.url`.
- also, make an effort to keep the Rack integration default as not
  preserving the URL base, restricting the transition code for the
  upcoming breaking change to that integration.

In practice this cop seems to be disabled as soon as we reach the limit.