feat: add data and axes transforms

[zao111222333]

I add a coordinate transform layer so series and reference lines can choose how their x/y values are interpreted before drawing. Normal data transforms run before the plot's axis scale, while Transform::axes() uses normalized plot coordinates where 0.0 is the low edge and 1.0 is the high edge.

This makes it possible to render data-converted series, fixed-position overlays, mixed data/axes coordinates, and transformed reference lines without changing the plot's global axis scale. Axes-coordinate geometry stays fixed during pan and zoom and is excluded from autoscale bounds.

Key changes:

• Add CoordinateSystem, Transform, and PositionTransform
• Support identity, affine, log, exp, composed, and axes-coordinate transforms
• Route AxisScale conversion through the shared transform implementation
• Add per-series transform APIs, including x/y-specific transforms and with_axes_transform
• Add transform support for VLine and HLine
• Apply transforms consistently in plot state, fills, highlights, tooltips, and both shader/canvas renderers
• Rebuild dynamic axes-coordinate geometry when camera or bounds change
• Display axes-coordinate tooltip values as percentages
• Add examples/transform.rs covering data, composed, axes, mixed-axis, and reference-line transforms:

Screen.Recording.2026-05-06.at.22.35.25.mov