fix(core): normalize signed Rect border bounds

[xuefei1313]

Summary

• Normalize Rect outer/inner border geometry from signed dimensions to physical bounds.
• Resolve x1/y1 fallback dimensions in attribute space while positioning paths from renderer-local coordinates.
• Add regressions for negative width, small rectangles, dx offsets, and non-degenerate inner borders.

Root cause

The border contribution assumed positive dimensions. For an x/x1 Rect with negative width, an outer-border expansion could invert the width and draw inside the physical bar. Its x1/y1 fallback also mixed attribute-space endpoints with renderer-local draw coordinates when offsets were applied.

Validation

• rushx test --runInBand in packages/vrender-core — 613 passed, 3 skipped.
• rush compile -t @visactor/vrender-core.
• Pre-push rush test --only tag:package — 7 related packages passed (existing warnings only).