build script output reruns skip UI

[dr-frmr]

Problem

Build.rs still wonky, see #480

Solution

Attempt to both make build script maximally sensitive to updates while skipping rebuild if only build-outputs have changed since last build. Seems to fix #480

Testing

build runtime,
change elements,
use SKIP_BUILD_FRONTEND flag,
etc

Docs Update

N/A

Notes

Let's test this on all the platforms we develop on frequently

[nick1udwig]

Doesn't seem to resolve #480 for me. I did:

kit f -r $PATH_TO_KINODE
cp -r ${PATH_TO_KINODE}/kinode/packages/docs ${PATH_TO_KINODE}/kinode/packages/mocks
# MacOs version of `sed`
sed -i '' 's/docs/mocks/' ${PATH_TO_KINODE}/kinode/packages/mocks/metadata.json

kit f -r $PATH_TO_KINODE

noting that it does not rebuild in the second kit f

Still -- it does seem like an improvement over current build.rs, hence approval 👍