feat: Separation and DeviceN color spaces (ISO 32000-2 §8.6.6-7) (Block F)

[ralflang]

Separation and DeviceN Color Spaces

• Part of Project: New-Style PDF library feature parity with legacy and path towards full ISO 32000-2 support #6
• Depends on feat: ICCBased color space (ISO 32000-2 §8.6.5) (Block F) #27 (ICCBased)

Implement Separation (single spot color) and DeviceN (multiple spot colors) color spaces.

Separation needs: colorant name, alternate space, tint transform function.
DeviceN needs: array of colorant names, alternate space, tint transform, optional attributes.

PdfSerializer emits /ColorSpace arrays with embedded tint transform functions (Type 2/4 PDF functions).

Used in print workflows for Pantone/spot color support.

Tests: Separation color space with tint transform in output, DeviceN with multiple colorants, fallback to alternate space.