Draw Data: Binary Tree View canvas width doubles with every level #129

Split out of #84 (case 1).

Problem

Binary Tree View reserves room for a full binary tree on both sides of the root, whatever the tree's actual shape. The canvas width is

(2^depth − 1) × 180 + 90   px   (BinaryTreeDrawer.draw: EY2 * NWidth * 2 + NWidth)

• Skewed trees waste most of it. The left-skewed example from Draw Data: potential issues with general tree view and binary tree view in data visualisation #84 is 2,790 px wide but only uses x = 0..1,530; the right half is empty.
• Deep trees probably can't render. Browsers cap a canvas dimension at around 32,767 px (not checked against current browser limits), so a binary tree of depth 8 or more, even a balanced one, likely shows nothing or misbehaves. That may be the "webpage issues" reported in Draw Data: potential issues with general tree view and binary tree view in data visualisation #84.

Example (left-skewed, depth 4):

draw_data([1, [[2, [[3, [[4, [None, [None, None]]], [None, None]]], [None, None]]], [None, None]]])

Possible fix

A compact layout that sizes each subtree by its actual width, for example the classic Reingold–Tilford tidy-tree algorithm, instead of spacing children by 2^depth. The canvas would then be computed from the real extent of the drawn nodes.

Found while investigating #84; the clipping bugs from that issue are fixed separately.