Check for Extension Updates in Parallel

[Haoming02]

Description

• a simple description of what you're trying to accomplish: Check the updates for all Extensions at once rather than one by one
  • On my system, checking updates for a dozen Extensions now only takes around 1 second, and after applying the updates, everything still works fine.
• a summary of changes in code: Make the for ext in exts: loop multi-threaded using the threading package

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests

---

Though, I'm not sure if the shared.state parts should be changed or not...

[w-e-w]

somehow I feel like the possibility of requesting hundreds of fetch to github is a bad idea
so I made some minor changes mainly rewriting it using ThreadPoolExecutor and setting a deafault limit of 16
and add some Atomic sections such as updating progress bar and Reporting on errors

do you think the number should be higher than 16?

fun fact I about 200 extension installed, (10 enabled, 190 disabled)

---

there is also the --update-all-extensions cli arg
which currently is not concurrent
if that is to be made concurrent I'm not sure using a setting value is a good idea