Add classes for coordinate spaces and transforms (#218)

New classes:

* Axis: simple data class storing a name, optional units, and optional scale
* CoordinateSpace: used to define coordinate spaces for spatial data
* CoordinateTransform: abstract base class for coordinate transforms
* AffineTransform: implementation for a generic affine coordinate transform
* ScaleTransform: implementation for a coordinate transform that scales axes (may be isotropic/uniform)
* IdentityTransform: implementation for an identity transform that only applies a name change to axes

---------

Co-authored-by: paul fisher <paul.fisher@tiledb.com>

python-spec/src/somacore/__init__.py

@@ -16,6 +16,13 @@
 
 from .base import SOMAObject
 from .collection import Collection
+from .coordinates import AffineTransform
+from .coordinates import Axis
+from .coordinates import CoordinateSpace
+from .coordinates import CoordinateTransform
+from .coordinates import IdentityTransform
+from .coordinates import ScaleTransform
+from .coordinates import UniformScaleTransform
 from .data import DataFrame
 from .data import DenseNDArray
 from .data import NDArray
@@ -61,4 +68,11 @@
     "AxisQuery",
     "ExperimentAxisQuery",
     "ContextBase",
+    "Axis",
+    "CoordinateSpace",
+    "CoordinateTransform",
+    "AffineTransform",
+    "ScaleTransform",
+    "UniformScaleTransform",
+    "IdentityTransform",
 )