* configs/configschema: fix missing "computed" attributes from NestedObject's ImpliedType
listOptionalAttrsFromObject was not including "computed" attributes in the list of optional object attributes. This is now fixed. I've also added some tests and fixed some panics and otherwise bad behavior when bad input is given. One natable change is in ImpliedType, which was panicking on an invalid nesting mode. The comment expressly states that it will return a result even when the schema is inconsistent, so I removed the panic and instead return an empty object.