cleanups and improvements to lagrange #3306

Job	Run time
nix	2m 23s
quick-build (supported, ubuntu-latest)	2m 46s
build (supported)	2m 49s
quick-build (latest, ubuntu-latest)	3m 16s
opam-build (supported, ubuntu-latest)	4m 16s
build (latest)	3m 24s
quick-build (dev, ubuntu-latest)	2m 45s
opam-build (latest, ubuntu-latest)	4m 28s
build (dev, --warnings)	2m 48s
opam-build (dev, ubuntu-latest)	3m 39s
doc-alectryon	0s
doc-dep-graphs	0s
coqchk	0s
doc-coqdoc	0s
doc-timing	0s
install	0s
deploy-doc	0s
delete-artifacts	5s
	32m 39s

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