#117 fix SPI tests by adding missing key/value type checks

Missing key/value type checks are fixed, but the hit rate test is still failing because hit rate is not yet implemented. I left that test as ignored and I opened #122 to track the missing implementation.
It looks fine to me. It's a `CacheAccessException` but rather a wiring issue in our code, or the user falling back to the raw type and "trying" to pollute the `Cache` with random type instances. It merely guards itself against the abuse.