Add a fold operation over finite maps, and associated lemmas #3967

Job	Run time
Fetch EasyCrypt External Projects Matrix	6s
EasyCrypt compilation (nix)	1m 13s
EasyCrypt compilation (opam)	2m 50s
Check EasyCrypt Libraries (unit)	2m 52s
Check EasyCrypt Libraries (stdlib)	6m 12s
Check EasyCrypt Libraries (examples)	4m 57s
Check EasyCrypt External Projects (xmss-fsai, https://github.com/MM45/FV-XMSS-EC, master, ., conf...	7m 54s
Check EasyCrypt External Projects (jasmin-eclib, https://github.com/jasmin-lang/jasmin, main, ecl...	3m 24s
Check EasyCrypt External Projects (xmss-acai, https://github.com/MM45/FV-XMSS-EC, master, ., conf...	8m 48s
Check EasyCrypt External Projects (cryptobox, https://gitlab.com/fdupress/ec-cryptobox, next, ., ...	3m 55s
Check EasyCrypt External Projects (sha3, https://gitlab.com/easycrypt/sha3, next, ., config/tests...	14m 8s
Check EasyCrypt External Projects (xsalsa20, https://gitlab.com/fdupress/ec-xsalsa, ec-main, ., c...	3m 21s
Check EasyCrypt External Projects (sphincsplus, https://github.com/MM45/FV-SPHINCSPLUS-EC, master...	20m 26s
Check EasyCrypt External Projects (set-status)	5s
Notification	6s
	1h 20m 17s

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