add `itv_closureE`, `itv_interiorE`, and helper lemmas #4960

Job	Run time
rocq-elpi	3m 13s
rocq-core	2m 36s
stdlib	3m 59s
coq	41s
coq-elpi	1m 1s
mathcomp-bigenough	0s
mathcomp-finmap	0s
hierarchy-builder	1m 44s
mathcomp	0s
mathcomp-classical	0s
mathcomp-reals	0s
mathcomp-analysis	0s
mathcomp-experimental-reals	-1s
mathcomp-reals-stdlib	0s
mathcomp-analysis-single	0s
mathcomp-analysis-stdlib	0s
	13m 13s

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