deserializeValueImpl

import mir.ion.value;
import mir.ion.exception;
import mir.bignum.integer;

auto data = IonValue([0x31, 0x07]).describe;
BigInt!128 value = void; // 256x64

assert(deserializeValueImpl(data, value) == IonErrorCode.none);
assert(value.sign);
assert(value.view.unsigned == 7);