fix: preserve indexed Boolean CopyBits semantics

[benletchford]

Cause

CopyBits routed Boolean source modes through RGB conversion even when the source and destination PixMaps had the same indexed depth and ColorTable. That discarded the source pixel-index bit pattern, so operations such as srcXor were no longer reversible and complementary sprite draws could leave palette artifacts.

Fix

• Detect shared explicit indexed color spaces at 2-, 4-, and 8-bit depths.
• Apply all eight Boolean source modes directly to source and destination pixel indices in that case.
• Mask complemented results to the active pixel depth.
• Keep foreground/background color conversion and palette translation for different color spaces and depths.
• Use the same behavior in both standard CopyBits execution paths.

Tests

• cargo fmt --check
• cargo test copy_bits_ (33 passed)
• cargo test trap::quickdraw::tests (628 passed)
• cargo test --lib (2,951 passed; 3 ignored)

Closes #563