Implement native TGA and DDS compatibility (#39)

README.md

@@ -129,5 +129,17 @@ constructors and resizers cap decoded images at 4096 by 4096 worth of pixels,
 codec adapters cap buffered encoded input at 64 MiB, and canonical
 interleaving accepts explicit row strides without exposing codec-library types
 through the core abstraction.
+The native TGA/Pfim-compatible path decodes uncompressed and RLE true-color,
+grayscale, and indexed TGA data with all descriptor orientations, plus bounded
+legacy and DX10 DDS packed luminance/RGB(A) layouts and BC1 through BC7 blocks.
+TGA output preserves the reference header, BGR(A) order, descriptor choice,
+alpha-only expansion, and deterministic trailing padding. File and stream
+inputs are capped before decoding, and all dimensions, packed rows, palettes,
+packets, masks, and block indices use checked arithmetic with positioned parse
+errors.
+Legacy and DX10 BC1 through BC5 decoding is built in. The default `dds-bc67`
+feature adds BC6H/BC7 decoding through the safe, pure-Rust `bcdec_rs` crate;
+disabling default features removes that optional dependency and makes those
+two formats return a typed unsupported-format error.
 The controlled audit aggregates every expected failure by standardized C#
 member ID and rejects unrelated fixture, assertion, compile, or symbol errors.