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.

Unit tests pass.