waffle unit: auto

When a waffle mark depicts large values, it might become invisible because the area for each "dot" becomes infinitesimal. This suggests that the default unit should be "auto" instead of 1, and adapt to the available area.

To avoid unwanted surprises, this should not be too progressive (we don't want this to kick in for values such as 0.001 or 1000), but only happen only if the base dot is infinitesimal or super-extra-huge. It should also only work with powers of 10 (or maybe powers of 1000).

It should also be shared between all waffle marks (but that should be OK given that it will be based on the available area = bandwidth × bar length). We might want a way to surface it to the user (something like an internal scale, maybe?).

Start by locating the waffle mark entry point and tracing how the current unit value determines dot size from the available area. Define and test the boundaries for automatic scaling, including supported powers and cases where scaling should not occur; the issue is done when large-value waffle marks remain visible without changing ordinary values unexpectedly.