Support uncompressed stripped RGB TIFF

[jcwal1516]

What changed

• recognize a narrow, validated subset of strip-based TIFF images
• expose conventional TIFFs through a synthetic 256x256 tile grid
• decode interleaved or separate 8-bit RGB sample planes with bounded full-image caching
• document the supported constraints and add regression coverage

Why

The generic TIFF reader previously accepted only tiled images, so valid conventional uncompressed RGB TIFF files failed as unsupported.

User impact

The viewer can open a single top-level, uncompressed 8-bit RGB TIFF with top-left orientation, no predictor, and contiguous or planar samples. Unsupported TIFF variants continue to fail explicitly.

Validation

• cargo test --locked generic_planar_stripped_rgb_tiff_opens_and_reads_synthetic_edge_tile
• cargo fmt --all -- --check
• cargo clippy --all-targets --locked -- -D warnings