gh-135567 Add customization to country code second-level domains in DefaultPolicy of lib http.cookiejar and update the default list of it

[LamentXU123]

Following the previous discussion, I've defined a class var self.slds, and add a attr additional_country_code_slds which is a set type (defaulting {}) and will be merged into the default set which is discussed before.

        well_known_slds = {"co", "ac", "com", "edu", "org", "net",
                        "gov", "mil", "int", "aero", "biz", "cat", "coop",
                        "info", "jobs", "mobi", "museum", "name", "pro",
                        "travel", "eu", "tv", "or", "nom", "sch", "web"}

Yeah I think customization is the true way to solve the problem, updating list in hard code is just not a good idea IMO.

What do you guys think? @picnixz @Zheaoli

Note that we could just update the list in hard code if the FR is rejected tho, which I think is not good. I know we could deal it in seperate issues but I think only support more domains doesn't sounds great,

So sry for all the noise i've made.

• Issue: Support more Second-Level Domain Names in lib http.cookiejar #135528

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📚 Documentation preview 📚: https://cpython-previews--135569.org.readthedocs.build/

• Issue: Add customization to country code second-level domains in DefaultPolicy of lib http.cookiejar #135567

Please do not laugh at the commit history, I am totally an idiot in late nights >_< (I've uploaded cookiejar.py to cookie.py lol)