Switch to treemacs-treelib. #224

Job	Run time
build (ubuntu-latest, 27.2, false)	1m 40s
build (ubuntu-latest, 28.2, false)	1m 56s
build (ubuntu-latest, 29.1, false)	1m 43s
build (macos-latest, 27.2, false)	3m 27s
build (macos-latest, 28.2, false)	3m 11s
build (macos-latest, 29.1, false)	3m 45s
build (windows-latest, 27.2, false)	2m 8s
build (windows-latest, 28.2, false)	2m 19s
build (windows-latest, 29.1, false)	2m 1s
build (ubuntu-latest, snapshot, true)	1m 30s
build (macos-latest, snapshot, true)	3m 33s
build (windows-latest, snapshot, true)	1m 19s
	28m 32s

Provide feedback