Lack user Agent, not using Conditional Requests

[manglewit]

Add-on version
Add-on version: 3.8

Describe the bug

1. Livemarks is not setting a User-agent that identifies itself, such as "Livemarks v3.8"
2. Livemarks is not using Conditional Requests. It is simply using Unconditional Requests all the time, which wastes bandwidth and server capacity

To Reproduce
Steps to reproduce the behaviour:
Run Livemarks against a feed that logs its behaviour. Examine the logs.

Expected behaviour

1. Livemarks should set a User-agent that identifies itself with a version number (or equivalent), such as "Livemarks v3.8"
2. Livemarks should use Conditional Requests - see https://rachelbythebay.com/fs/help.html for details,

Extra context
The website:
https://rachelbythebay.com is offering a (free) logging service so you can see how well behaved your feed reader is. More details at https://rachelbythebay.com/w/2024/05/30/fs/

Note that I like Livemarks, and find that the UI does what I expect - minimalist but functional. I'm worried that not using Conditional Requests means that some services could block access for not being a good netizen. I don't want to be forced to use a different utility.

[evilpie]

See also #436.

I am sympathetic to the idea of not causing unnecessary load for servers, but we also have to consider the needs/wants of the user.