fix: fetchNoCors and http_request data handling

[FrogTheFrog]

Please tick as appropriate:

• I have tested this code on a steam deck or on a PC
• My changes generate no new errors/warnings
• This is a bugfix/hotfix
• This is a new feature

Description

This PR solves 4 problems:

1. fetchNoCors does not prefix explicitly specified headers which can later be overwritten or deleted by http_request handler. Arguably, if the user has specified headers explicitly then they must be sent out in the end.
2. http_handler would automatically decompress received data, but not intended to do so. Decompressing is now delegate to JS engine.
3. fetchNoCors would cache the the request incorrectly under a generic http://127.0.0.1:1337/fetch url if the server response asks it to. Caching could be disabled completely for fetchNoCors, however another approach was taken - url is added as a query parameter so that the cache is associated correctly with the provided url.
4. http_handler no longer has special headers for auth and url, and are now parsed from query only. Replaced the get methods with access operators so that the exception is thrown early on an ill-formed url to avoid confusing exceptions down the line.