feat: Pattern color space and tiling patterns (ISO 32000-2 §8.7.3) (Block F)

[ralflang]

Pattern Color Space and Tiling Patterns

• Part of Project: New-Style PDF library feature parity with legacy and path towards full ISO 32000-2 support #6
• Depends on feat: Shading patterns and gradients (ISO 32000-2 §8.7.4) (Block F) #29 (shading infrastructure)

Implement tiling patterns (Type 1) - repeating content cells painted as a color space.

TilingPattern wraps a content stream + BBox + XStep/YStep + paint type.
Reuses Form XObject concepts for the pattern cell content.

Pattern color space registered in /ColorSpace, pattern object in /Pattern resource dictionary.

ContentStreamBuilder: setFillPattern() / setStrokePattern().
PdfWriter: defineTilingPattern() + use via color API.

Tests: tiling pattern renders repeating cells, pattern resources in output, colored vs uncolored patterns.