Fix: Multi-line axis/tick labels

[brenocq]

Fixes #630

Summary

Fixes incorrect axis padding calculation when tick labels or axis labels contain
multiple lines (using \n).

Problem

When using custom formatters that output multi-line tick labels, the axis padding
calculation doesn't account for the actual height of the labels, causing:

• Plot titles to overlap with axis labels
• Axis labels to extend outside the axis area
• Incorrect spacing between subplots

Root cause: X-axis padding was calculated before X-axis ticks were generated,
so axis.Ticker.MaxSize.y was 0 or a default value. Additionally, axis label
height was assumed to be single-line.

Solution

1. Recalculate X-axis padding after tick generation - Added a second call to
   PadAndDatumAxesX() after ticks are generated (when actual tick label sizes are
   available), while preserving the title padding
2. Use CalcTextSize() for axis labels - Properly measure axis label height
   instead of assuming single-line (T + P), allowing multi-line axis labels to work
   correctly

Before

Here's after the fix to take into account the tick label height and X axis label height