Let Manager subdivisions be numpy array

numpy arrays don't (and likely won't) fulfill the Sequence
interface
numpy/numpy#2776
numpy/numpy#7315

The array gets converted down to a tuple any way, and each element
must be an integer too.

Unit test modified to allow this behavior.

src/hydep/manager.py

@@ -155,7 +155,7 @@ def _validateSubsteps(self, divisions):
             if divisions <= 0:
                 raise ValueError(f"Divisions must be positive integer, not {divisions}")
             return FakeSequence(divisions, maxallowed)
-        if isinstance(divisions, Sequence):
+        if isinstance(divisions, (numpy.ndarray, Sequence)):
             if len(divisions) != maxallowed:
                 raise ValueError(
                     "Number of divisions {} not equal to number of time "

tests/test_manager.py

@@ -130,6 +130,15 @@ def test_managerSubsteps(simpleChain):
     divset = {safeargs.divisions * x for x in range(1, ntimesteps + 1)}
     assert len(divset) == ntimesteps
 
+    # Test that numpy arrays are good
+    arraySubs = hydep.Manager(
+        safeargs.chain,
+        safeargs.timesteps,
+        safeargs.power,
+        numpy.arange(1, ntimesteps + 1),
+    )
+    assert arraySubs.substeps == tuple(range(1, ntimesteps + 1))
+
     with pytest.raises(TypeError):
         hydep.Manager(safeargs.chain, safeargs.timesteps, safeargs.power, divset)