chore(ci): Speed up critical path of CI

We've decided to try using some of our funding to speed up CI.
kbknapp has experience with buildjet in the past which allows us to keep
our Actions and switch out our runners.

As we are charged for `num_cores * time`, increasing core counts could
decrease time, both helping us and keeping costs down.
I chose 8 cores (an upgrade over `ubuntu-latest`s 2 cores) as kbknapp
knew someone who benchmarked things for Rust/Python and found that a
good fit.

I only switched a subset of jobs over to buildjet to focus on jobs where
most of the time is spent on highly parallelizable operations.
Buildjet dropped our Linux test jobs from 8-9min to 2-3min.
The checks and UI-test jobs only improved by 30s-1min each, so I left
them out.
We can iterate as we go.

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
         build: [linux, windows, mac, minimal, default, next]
         include:
         - build: linux
-          os: ubuntu-latest
+          os: buildjet-8vcpu-ubuntu-2204
           rust: "stable"
           features: "full"
         - build: windows