roo_display 3.4.0

• Fix composition rendering across raster and streaming paths, including first-layer blending, clipped masks, empty inputs, long spans, skipped pixels, and background handling.
• Improve composition performance by skipping hidden layers and redundant mask samples, filling uniform regions directly, and allocating buffers only for surviving inputs.
• Bound raster and filter scratch memory. Enforce the 16-input StreamableStack limit with capacity checks; retain support for arbitrary input counts in RasterizableStack.
• Add reusable composition APIs for replacing inputs and retaining reserved storage, plus documentation on source lifetimes, caching, and group opacity.
• Accelerate clipped bitmap and RLE reads, stop PNG decoding after the last visible row, and batch transformed uniform fills. Fix RleImage<Alpha8> compilation and packed-RLE uniform-run detection.
• Expose gradient opacity and uniform-color hints. Correct SourceAtop rounding and transparent-color handling, and honor ROO_DISPLAY_BLENDING_PRECISION overrides.
• Expand composition regression tests, benchmarks, and heap/ESP32 stack measurements.
• Upgrade roo_io to 2.4.1 and the Bazel development dependency roo_fonts_basic to 1.0.6.

Full Changelog: 3.3.2...3.4.0