Jellyflow 0.2.0

Added

• Added the built-in tidy_tree layout engine and made LayoutPresetBuilder::tree() target it by
  default.
• Added Criterion benchmarks for built-in layout engines.
• Added LayoutPresetBuilder for workflow, tree, radial mind-map, and freeform mind-map layout
  request presets.

Changed

• Consolidated repeated native layout projection and result-building helpers.