Blitz: `blitz start` is significantly slower to start than `next dev`

[flybayer]

What is the problem?

Next.js re-uses it's own build cache between next dev invocations so that subsequent runs of next dev start extremely fast.

But the problem is that we are deleting the entire .blitz cache folder, including the next.js cache. This means that blitz start is always slow to start.

Steps to Reproduce

1. Run blitz start several times and notice the start time.
2. Run yarn next .blitz/caches/dev several times and notice the much faster start time

Versions

0.22.0

cc @ryardley

[ryardley]

Be happy jump on this - I have had a plan for this for a while.