gh-127753: make the proxies handling of urllib.request cacheable

[NewUserHa]

this code makes proxy_bypass_registry is also cacheable, to avoid repeating read the registry of windows.

and also makes the comment about CVE of getproxies_environment() together and more obviously

• Issue: optimize code for proxy handling of urllib.request  #127753

[ZeroIntensity]

I think this needs a blurb entry.

[NewUserHa]

actually, this structure of these functions feels no straightforward, new comers may do not know if use the original proxy_bypass() or getproxies(),
or use getproxies_environment() and getproxies_registry() and proxy_bypass_registry() and getproxy_bypass_registry() to build its own cacheable proxy_bypass() or getproxies() to avoid repeat reading from os.

But it looks not good to change or delete the original behavior of the original proxy_bypass() or getproxies() functions, so to make new users know how to correctly use and cache it if the users want to use, should re-arrange or re-name these original functions, or just add documents for it?

[ZeroIntensity]

Sure, if the old APIs are too broken to improve, then add something new.