Improves on Fetch.ts

1. Adjusted UA string to my UA string on my Pixel5A running Android 13. User Agents have become more obscured and generic, so having a very specific UA string will start to stand out.
2. Implemented the capacity to specify a unique user agent string, or remove it entirely. Now done by switching line order and adding comments.

Why, you ask, would I want to remove a user agent string? Because if there's no UA string you can get the page without lazy loading images, which can potentially make or break pulling images. Sure, I can just use a raw fetch, but that doesn't have cloudflare bypass. (Specifically for ReaperScans)
This is the best of both worlds, while still functioning as expected with existing scripts.

Theoretically fixes LNReader/lnreader-plugins#473 but webview crashes my emulator.
Did several test loads to see if I saw any unexpected errors produced by this conversion, but wasn't able to find any.

Good news: Throws proper errors when cloudflare can't be bypassed instead of giving broke chapters
Bad news: I don't think it's getting the cookie for the bypass.