Issue #503: apply axisTitlePadding to right-side Y axis title

[timmolter]

Fixes #503.

Problem

axisTitlePadding opens a gap between the axis title and its tick labels on the left Y axis, but not on a right-side (second) Y axis. On the right, the padding was spent as dead space on the outer edge of the title (toward the chart border), leaving the title jammed against its tick numbers no matter how large the padding was set — including via a custom Theme extends AbstractBaseTheme overriding getAxisTitlePadding(), as in the original report.

Root cause

In AxisTitle.paint(), the left branch bakes the padding into the title bounds width, which the tick labels are then offset by — so the padding lands between the title and the labels. The right (onRight) branch placed the title at tick.x + tick.width + textHeight with no + padding, so no gap was created; the padding only extended the bounds outward into unused space.

Fix

• Push the right-side title outward past the tick labels by axisTitlePadding, so the padding forms a title↔tick-label gap mirroring the left side.
• Shift the right-side bounds origin inward by the same amount, keeping the reserved column width unchanged (no change to getYAxisWidthHint).

Single-file change in AxisTitle.java; left-axis and single-axis rendering are untouched.

Tests

• RegressionIssue503Test — renders with title text and tick labels in distinct colors, locates them by pixel, and asserts the title↔tick-label gap grows by ~100px when padding goes 5→105 on both left and right axes. Fails on the old code (right gap stayed fixed), passes now.
• Full xchart suite: 141 tests green.

Manual verification

TestForIssue503 demo (added) — a custom AbstractBaseTheme subclass with a large getAxisTitlePadding(), one left + one right Y axis. Before: only the left title had a gap; after: both sides respond to the padding in lockstep.

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