feat: upgrade to uv 0.8.20 and get rid of non-async build dispatch calls

[tdejager]

This PR does three things:

1. Upgrades to uv 0.8.20, and makes sure the code is compatible
2. Get rid of the weird block_on call that was sometimes making tokio hang
3. Start using and sharing some structs that we were re-creating like the workspace cache, as well as be more consistent what we pass through. For example exclude_newer was being used in resolution but not in installation, which seems just wrong.

Fixes: #3974

[tdejager]

Fixes: #3974

Also again thanks @zanieb, for making this possible! Something kind-of ugly had to be merged to make this possible :)

Also, @lucascolley thanks for testing!