Remove outdated backend classes

E.g. NoSymmetryNumpyBackend
We introduced them back when backends had a diamond inheritance structure
of a block backend and a symmetry backend.
Since we changed that, these specialized classes are unnecessary.

cyten/backends/array_api.py

@@ -6,16 +6,12 @@
 from __future__ import annotations
 
 from .abstract_backend import BlockBackend, Block
-from .no_symmetry import NoSymmetryBackend
-from .fusion_tree_backend import FusionTreeBackend
-from .abelian import AbelianBackend
 from ..dtypes import Dtype
 
 import numpy as np
 
 
-__all__ = ['ArrayApiBlockBackend', 'NoSymmetryArrayApiBackend', 'AbelianArrayApiBackend',
-           'FusionTreeArrayApiBackend']
+__all__ = ['ArrayApiBlockBackend']
 
 
 # TODO provide an example...
@@ -294,27 +290,3 @@ def block_enlarge_leg(self, block: Block, mask: Block, axis: int) -> Block:
 
     def block_stable_log(self, block: Block, cutoff: float) -> Block:
         return self._api.where(block > cutoff, self._api.log(block), 0.)
-
-
-class NoSymmetryArrayApiBackend(NoSymmetryBackend):
-    """TODO"""
-
-    def __init__(self, api_namespace):
-        block_backend = ArrayApiBlockBackend(api_namespace)
-        NoSymmetryBackend.__init__(self, block_backend=block_backend)
-
-
-class AbelianArrayApiBackend(AbelianBackend):
-    """TODO"""
-
-    def __init__(self, api_namespace):
-        block_backend = ArrayApiBlockBackend(api_namespace)
-        AbelianBackend.__init__(self, block_backend=block_backend)
-
-
-class FusionTreeArrayApiBackend(FusionTreeBackend):
-    """TODO"""
-
-    def __init__(self, api_namespace):
-        block_backend = ArrayApiBlockBackend(api_namespace)
-        FusionTreeBackend.__init__(self, block_backend=block_backend)

cyten/backends/numpy.py

@@ -5,14 +5,10 @@
 import numpy as np
 import scipy
 
-from .abelian import AbelianBackend
 from .abstract_backend import BlockBackend, Block
-from .no_symmetry import NoSymmetryBackend
-from .fusion_tree_backend import FusionTreeBackend
 from ..dtypes import Dtype, _numpy_dtype_to_cyten, _cyten_dtype_to_numpy
 
-__all__ = ['NumpyBlockBackend', 'NoSymmetryNumpyBackend', 'AbelianNumpyBackend',
-           'FusionTreeNumpyBackend']
+__all__ = ['NumpyBlockBackend']
 
 
 class NumpyBlockBackend(BlockBackend):
@@ -292,26 +288,5 @@ def zero_block(self, shape: list[int], dtype: Dtype, device: str = None) -> Bloc
         return np.zeros(shape, dtype=self.backend_dtype_map[dtype])
 
 
-class NoSymmetryNumpyBackend(NoSymmetryBackend):
-    """TODO"""
-
-    def __init__(self):
-        NoSymmetryBackend.__init__(self, block_backend=NumpyBlockBackend())
-
-
-class AbelianNumpyBackend(AbelianBackend):
-    """TODO"""
-
-    def __init__(self):
-        AbelianBackend.__init__(self, block_backend=NumpyBlockBackend())
-
-
-class FusionTreeNumpyBackend(FusionTreeBackend):
-    """TODO"""
-
-    def __init__(self):
-        FusionTreeBackend.__init__(self, block_backend=NumpyBlockBackend())
-
-
 def _svd_gesvd(a):
     raise NotImplementedError  # TODO

cyten/backends/torch.py

@@ -4,14 +4,10 @@
 from numpy import prod
 import numpy
 
-from .abelian import AbelianBackend
 from .abstract_backend import BlockBackend, Block
-from .no_symmetry import NoSymmetryBackend
-from .fusion_tree_backend import FusionTreeBackend
 from ..dtypes import Dtype
 
-__all__ = ['TorchBlockBackend', 'NoSymmetryTorchBackend', 'AbelianTorchBackend',
-           'FusionTreeTorchBackend']
+__all__ = ['TorchBlockBackend']
 
 
 class TorchBlockBackend(BlockBackend):
@@ -338,27 +334,3 @@ def synchronize(self):
     def zero_block(self, shape: list[int], dtype: Dtype, device: str = None) -> Block:
         return torch_module.zeros(list(shape), dtype=self.backend_dtype_map[dtype],
                                   device=self.as_device(device))
-
-
-class NoSymmetryTorchBackend(NoSymmetryBackend):
-    """TODO"""
-
-    def __init__(self, default_device: str = 'cpu'):
-        block_backend = TorchBlockBackend(default_device=default_device)
-        NoSymmetryBackend.__init__(self, block_backend=block_backend)
-
-
-class AbelianTorchBackend(AbelianBackend):
-    """TODO"""
-
-    def __init__(self, default_device: str = 'cpu'):
-        block_backend = TorchBlockBackend(default_device=default_device)
-        AbelianBackend.__init__(self, block_backend=block_backend)
-
-
-class FusionTreeTorchBackend(FusionTreeBackend):
-    """TODO"""
-
-    def __init__(self, default_device: str = 'cpu'):
-        block_backend = TorchBlockBackend(default_device=default_device)
-        FusionTreeBackend.__init__(self, block_backend=block_backend)