test(charts): measure the pie, the bar tooltip and the X label rotation (#1160, #1161) - #1248

Closes #1160
Refs #1161

Changes

• fix(charts): pie without legend, colours repeat, fixed radius #1160: the pie is measured at 600 and 1600 px. Its size grows with the pane, and its slice radius follows the outer radius formula. The 30-category Top 8 + Other test already existed.
• ui(charts): themed tooltips, number formatting, label overflow, titles and axis names #1161: the bar tooltip shows 1,234,567 and uses the theme popover colour. Forty X labels reserve the rotated room (52 px), three labels do not (28 px).

Not covered (#1161 stays open)

• Tooltip readability in the light, dark and imported VS Code themes. The test checks the colour the code picks, in the default test theme only.
• The 1.2M axis label is covered by chart_format_test.dart, not by a test of the axis wiring.
• Label overlap is checked through the rotation rule, not by measuring the rendered labels.