Extend EndianNat to convert from nat #7770

Job	Run time
fmt	1m 18s
test-and-release-macos (record-history)	4m 5s
test-and-release-macos (no-std)	3m 58s
test-and-release-macos	17m 30s
test-and-release-macos (no-alloc)	4m 1s
smoke-test-and-release-macos-x86	22m 50s
smoke-test-and-release-windows	9m 0s
test-and-release-macos (cvc5)	4m 48s
smoke-test-and-release-linux	7m 52s
test-and-release-macos (singular)	5m 18s
release	0s
	1h 20m 40s

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