Refactor jupyenv #913

Job	Run time
Build jupyterlab (no kernels)	6m 50s
Build example-bash-minimal kernel	7m 8s
Build example-c-minimal kernel	6m 2s
Build example-elm-minimal kernel	6m 1s
Build example-go-minimal kernel	6m 21s
Build example-haskell-minimal kernel	12m 39s
Build example-javascript-minimal kernel	5m 7s
Build example-julia-minimal kernel	12m 32s
Build example-nix-minimal kernel	5m 37s
Build example-ocaml-minimal kernel	13m 36s
Build example-postgres-minimal kernel	8m 38s
Build example-python-minimal kernel	6m 56s
Build example-python-native kernel	5m 21s
Build example-python-science kernel	23m 17s
Build example-python-stable kernel	7m 21s
Build example-r-minimal kernel	5m 52s
Build example-rust-minimal kernel	5m 49s
Build example-scala-minimal kernel	5m 35s
Build example-typescript-minimal kernel	59m 0s
Build example-zsh-minimal kernel	8m 18s
Build devshell	0s
Build docs	0s
Build all kernels	0s
Test a template	0s
	3h 38m 0s

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