This change adds unit tests that cover the `@spina` decorator, testing all options and behaviors. While working on this, the following issues were found and fixed: * Instances created from a Spina class were lacking the typing to access Spina state and methods. * `__spinaOptions` wasn't marked readonly (fixing this required adding a new `MutableSpinaClass` so class prep could set this option). * `__spinaOptions` was always duplicated, wasting memory, since we weren't checking for emptiness correctly. * `automergeAttrs` retained attributes that were skipped. * Wrong names for classes could be used. * `__super__` wasn't read-only.