Port DDDisplay__BlitStippled (per-pixel checkerboard XOR pattern) and
DDDisplay__BlitTiled (horizontal sprite tiling) to pure Rust, eliminating
fallthrough to the original WA code for these modes.
Slot 19 (BlitSprite) now only falls through for bitmap sprites.
Slot 20 (DrawScaledSprite) has no fallthrough at all.
Adds 6 snapshot tests (4 stippled + 2 tiled) validated against WA ground
truth, and consolidates snapshot capture into a single OPENWA_CAPTURE_SNAPSHOTS
env var.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
