* Adds support for casting from `bool` -> `float32`.  Seems like a very common operation that is required in many places.
 * Fix bool register definition for vector operations
   * Use `vcc_lo` instead of `vcc` which seems to be required since it's configured to use wavefront_size=32
 * Add vector support for some places that were scalar only in register definition and comparison ops
 * Fix some issues in what seems to be defunct `external_test_image.py`
   * Some tests still don't pass for other reasons, but it at least runs now and one broken test is now fixed

 * Unify multi-registor code between dtypes and combine with single-register allocation since they're all untyped registers at the end of the day