Add a Stack (proposal definition) and a heater w.i.p. example

examples/complex/heater/heater.py

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+import os
+
+import numpy as np
+
+import classy_blocks as cb
+from classy_blocks.construct.flat.sketches.disk import WrappedDisk
+
+# TODO: direct imports!
+from classy_blocks.construct.shape import ExtrudedShape
+from classy_blocks.construct.stack import RevolvedStack
+
+wire_diameter = 10
+wire_length = 100
+bend_radius = 2 * wire_diameter
+
+
+mesh = cb.Mesh()
+
+heater_xs = WrappedDisk([0, 0, 0], [0, -bend_radius / 2, -bend_radius / 2], wire_diameter / 2, [1, 0, 0])
+straight_1 = ExtrudedShape(heater_xs, wire_length)
+
+curve = RevolvedStack(straight_1.sketch_2, np.pi / 4, [0, 0, 1], [wire_length, bend_radius, 0], 4)
+for shape in curve.shapes:
+    mesh.add(shape)
+
+    for i in range(3):
+        for op in shape.operations:
+            op.chop(i, count=10)
+
+for i in range(3):
+    for op in straight_1.operations:
+        op.chop(i, count=10)
+
+mesh.add(straight_1)
+
+mesh.write(os.path.join("..", "..", "case", "system", "blockMeshDict"), debug_path="debug.vtk")

src/classy_blocks/construct/stack.py

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+from typing import List
+
+from classy_blocks.construct.flat.sketch import Sketch
+from classy_blocks.construct.operations.loft import Loft
+from classy_blocks.construct.shape import LoftedShape, RevolvedShape
+from classy_blocks.types import PointType, VectorType
+
+
+class Stack:
+    """A collection of topologically similar Shapes,
+    stacked on top of each other."""
+
+    shapes: List[LoftedShape] = []
+
+    @property
+    def grid(self) -> List[List[List[Loft]]]:
+        """Returns a 3-dimensional list of operations;
+        first two dimensions within a shape, the third along the stack"""
+        return [shape.grid for shape in self.shapes]
+
+
+class RevolvedStack(Stack):
+    """Revolved shapes, stacked around the given center"""
+
+    def __init__(self, base: Sketch, angle: float, axis: VectorType, origin: PointType, repeats: int):
+        for _ in range(repeats):
+            shape = RevolvedShape(base, angle, axis, origin)
+            self.shapes.append(shape)
+            base = shape.sketch_2