Use URI.open() instead of open(), plus properly escape query string parameters

[morgant]

This replaces deprecated uses of open() with URI.open() for compatibility with Ruby 3.x where it now causes fatal errors (see Issue #3.) It also adds some uses of CGI.escape() to ensure that the requested URL's query string parameters are properly escaped and not accidentally mixed with the WayBack Machine's query string parameters.

[morgant]

I have since noticed I incorrectly introduced CGI.escape() call in WaybackMachineDownloader#download_file, which causes unexpected issues if the requested file/path includes a query string. I have reverted that particular use, leaving it in-place in #get_raw_list_from_api, where it is still necessary.