fix tree flatten and unflatten error

brainunit/_base.py

@@ -958,9 +958,9 @@ class Quantity(object):
   def __init__(
       self,
       value: Any,
-      dtype: bst.typing.DTypeLike = None,
+      dtype: Optional[bst.typing.DTypeLike] = None,
       dim: Dimension = DIMENSIONLESS,
-      unit: 'Unit' = None,
+      unit: Optional['Unit'] = None,
   ):
     scale, dim = _get_dim(dim, unit)
 
@@ -995,6 +995,9 @@ def __init__(
     elif isinstance(value, (jnp.number, numbers.Number)):
       value = jnp.array(value, dtype=dtype)
 
+    elif isinstance(value, (jax.core.ShapedArray, jax.ShapeDtypeStruct)):
+      value = value
+
     else:
       raise TypeError(f"Invalid type for value: {type(value)}")
 
@@ -1464,22 +1467,22 @@ def _binary_operation(
         Whether to do the operation in-place (defaults to ``False``).
     """
     other = _to_quantity(other)
-    other_unit = None
+    other_dim = None
 
     if fail_for_mismatch:
       if inplace:
         message = "Cannot calculate ... %s {value}, units do not match" % operator_str
-        _, other_unit = fail_for_dimension_mismatch(self, other, message, value=other)
+        _, other_dim = fail_for_dimension_mismatch(self, other, message, value=other)
       else:
         message = "Cannot calculate {value1} %s {value2}, units do not match" % operator_str
-        _, other_unit = fail_for_dimension_mismatch(self, other, message, value1=self, value2=other)
+        _, other_dim = fail_for_dimension_mismatch(self, other, message, value1=self, value2=other)
 
-    if other_unit is None:
-      other_unit = get_unit(other)
+    if other_dim is None:
+      other_dim = get_unit(other)
 
-    new_unit = unit_operation(self.dim, other_unit)
+    new_dim = unit_operation(self.dim, other_dim)
     result = value_operation(self.value, other.value)
-    r = Quantity(result, dim=new_unit)
+    r = Quantity(result, dim=new_dim)
     if inplace:
       self.update_value(r.value)
       return self
@@ -2315,23 +2318,23 @@ def tree_flatten(self) -> Tuple[jax.Array | numbers.Number, Any]:
     Tree flattens the data.
 
     Returns:
-      The data and the unit.
+      The data and the dimension.
     """
-    return self.value, self.dim
+    return (self.value,), self.dim
 
   @classmethod
-  def tree_unflatten(cls, unit, value) -> 'Quantity':
+  def tree_unflatten(cls, dim, value) -> 'Quantity':
     """
     Tree unflattens the data.
 
     Args:
-      unit: The unit.
+      dim: The dimension.
       value: The data.
 
     Returns:
       The Quantity object.
     """
-    return cls(value, dim=unit)
+    return cls(*value, dim=dim)
 
   def cuda(self, deice=None) -> 'Quantity':
     deice = jax.devices('cuda')[0] if deice is None else deice