* perf(engine): replace linear scans that made document-sized inputs quadratic
enum_of re-classified the whole string for every character; widget names,
comment mentions and devcompare's common siblings each searched a growing
Vec; data.fill's export names and codegen's class names retried every
suffix from 2 against a list, cubic in the number of copies of one name;
and a batch rename template had no length cap although it is expanded
again for every match.
* address review: report the pattern in its own length error
A widget description can have a line, 100 long and black and 1 thick unless told
otherwise, and an SVG that comes in as locked layers, scaled to fit a size and
within the widget's 256 layers. The Counter example uses both.
* M11: a widget opens its plugin's panel (plugin API 5)
Gap 6: a widget callback's ui_show opens the plugin's panel and keeps the module loaded; the panel's callbacks get the widget's id and state and redraw it in the same undo step. Older plugins' ui_show from a widget still opens nothing. The Counter example sets its count from a panel.
* M11: open_panel takes its opener as one value