Fix: negative tick_mark_size now only affects tick direction, not labels

[chantakan]

Summary

This PR fixes the behavior of negative tick_mark_size values. Previously, using a negative value caused labels and axis descriptions to move inside the plot area, overlapping with the chart content.

Expected Behavior (after this fix)

When using negative tick_mark_size, only the tick marks should point inward (into the plot area), while labels remain outside. This matches the expected behavior similar to matplotlib's ax.tick_params(direction='in').

Previous Behavior (bug)

• Labels moved into the plot area
• Axis descriptions overlapped with numeric labels
• White label backgrounds hid grid lines

Changes

• Labels are now always positioned outside the plot area regardless of tick direction
• Axis lines are always drawn on the outer edge
• Inward tick marks are drawn on the plot area using strip_coord_spec()
• Outward tick marks continue to work as before

Testing

• All 81 unit tests pass
• All 49 doc tests pass
• Visually verified with test examples

Fixes #716

[chantakan]

Screenshots

Before (bug): Labels move inside with negative tick_mark_size

After (fix): Only tick marks point inward, labels stay outside