Refactor jupyenv #915

Job	Run time
Build jupyterlab (no kernels)	8m 52s
Build example-bash-minimal kernel	6m 9s
Build example-c-minimal kernel	6m 14s
Build example-elm-minimal kernel	5m 44s
Build example-go-minimal kernel	5m 11s
Build example-haskell-minimal kernel	10m 38s
Build example-javascript-minimal kernel	5m 16s
Build example-julia-minimal kernel	13m 46s
Build example-nix-minimal kernel	5m 33s
Build example-ocaml-minimal kernel	13m 48s
Build example-postgres-minimal kernel	7m 24s
Build example-python-minimal kernel	8m 41s
Build example-python-native kernel	5m 27s
Build example-python-science kernel	6m 26s
Build example-python-stable kernel	9m 9s
Build example-r-minimal kernel	5m 50s
Build example-rust-minimal kernel	7m 33s
Build example-scala-minimal kernel	5m 30s
Build example-typescript-minimal kernel	59m 36s
Build example-zsh-minimal kernel	8m 55s
Test a template	1m 15s
Build devshell	1m 7s
Build all kernels	17m 28s
Build docs	1m 4s
	3h 46m 36s

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