Add support for RFC 2822 in DateTime

[CleverSource]

This adds support for RFC 2822 to the DateTime library so dates in the RFC 2822 format can be parsed e.g. date headers when making requests with the Net library.

I propose a function such as fromDate is added as well, which will attempt to parse both an RFC 3339 date and RFC 2822 date, returning whichever does not fail. Erroring if neither a RFC 3339 date or RFC 2822 can't be returned. I have omitted this from the PR unless maintainers approve.

At the moment the following is the best alternative, which is why I propose this is implemented.

local Net = require("@lune/net")
local DateTime = require("@lune/datetime")

local response = Net.request {
    url = "https://google.com"
}

local date, month, year, time =
    response.headers.date:match("(%d%d?) (%a%a%a) (%d%d%d%d) (%d%d:%d%d:%d%d)")
local months = {
    Jan = 1,
    Feb = 2,
    Mar = 3,
    Apr = 4,
    May = 5,
    Jun = 6,
    Jul = 7,
    Aug = 8,
    Sep = 9,
    Oct = 10,
    Nov = 11,
    Dec = 12
}
local dateNow = DateTime.fromUniversalTime({
    year = year,
    month = months[month],
    day = date,
    hour = time:match("(%d%d):%d%d:%d%d"),
    minute = time:match("%d%d:(%d%d):%d%d"),
    second = time:match("%d%d:%d%d:(%d%d)")
}).unixTimestampMillis

print(dateNow)