Don't change the state of a 'request' entity using while the '#pagy_url_for' method for calendar pagination

[PyrinAndrii]

This PR fixes a bug that I faced trying to implement the calendar pagination.

Simple explanation:

While doing the calendar pagination I'm getting the next error expected :page >= 1; got "__pagy_page__"

The bug:

I think it was added to the pagy_url_for method in this commit, where we assign the request.Get object to the query_params variable and later change this object in the pagy_set_query_params method, so when after it we execute the pagy_url_for again the request.Get object is different and generates us broken URL.

How I'm reproducing it in my Rails app

• add gem 'pagy', '~> 8.1', '>= 8.1.2' to my Gemfile (Rails project)
• include Pagy::Frontend in ApplicationHelper
• include Pagy::Backend in my controller
• add @calendar, @pagy, @meals = pagy_calendar(collection, year: { }, month: { }, day: { }) in my action (e.g. index)
• add several pagy_nav... in your view. For example <%== pagy_nav(@calendar[:year]) %> & <%== pagy_nav(@calendar[:month]) %>

Check the bug in the playground

The bug is reproducible via Pagy Playground. Look at the images below as the proof:

1. Check generated links before the fix
2. Check generated links after the fix

[ddnexus]

🙏🏻 Thank you for the bug report and fix! Brilliant help from Lviv! 🇺🇦

Sorry for the bug. It originated from 2 things:

1. The query_params started from an assignation like request.GET.merge..., so it was set as a new object, and the commit changed it, forgetting to clone it first
2. We are missing tests for that, because the tests are currently passing 🤦 (and I don't run all the playground apps manually each time)

I am going to release the fix today, and try to add the tests ASAP.
Thank you!

[PyrinAndrii]

No problem, happy to help 👍.
Thank you for such a handy gem.