Extend EndianNat to convert from nat #7772

Job	Run time
smoke-test-and-release-macos-x86	13m 57s
smoke-test-and-release-windows	9m 39s
fmt	1m 4s
smoke-test-and-release-linux	7m 58s
test-and-release-macos (record-history)	4m 51s
test-and-release-macos (no-std)	3m 13s
test-and-release-macos (no-alloc)	3m 15s
test-and-release-macos (cvc5)	4m 16s
test-and-release-macos	24m 10s
test-and-release-macos (singular)	4m 43s
release	0s
	1h 17m 6s

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