vstd: Add missing cases for lemma2_to64 #6092

Job	Run time
fmt	56s
smoke-test-and-release-macos-x86	10m 5s
smoke-test-and-release-windows	8m 52s
smoke-test-and-release-linux	6m 24s
test-and-release-macos	11m 29s
test-and-release-macos (record-history)	2m 56s
test-and-release-macos (no-std)	2m 30s
test-and-release-macos (no-alloc)	2m 58s
test-and-release-macos (singular)	3m 14s
test-and-release-macos (cvc5)	2m 16s
release	0s
	51m 40s

Provide feedback