Carry #1636: document test-corpus --pixls

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UHgFEHEsefoQoBParH47JA

xtask/src/main.rs

@@ -29,9 +29,10 @@ commands:
                   show where test corpora live and their pins (xtask/src/corpus_pins.rs), or fetch
                   them into corpus/ (pinned commits, sha256-verified; --all = every corpus but pixls,
                   --photoshop --local copies from ../photocraft-corpus or $PHOTOCRAFT_CORPUS_REPO)
-  test-corpus [-p <crate>]... [--changed] [--local] [-- <test args>]
+  test-corpus [-p <crate>]... [--changed] [--pixls] [--local] [-- <test args>]
                   fetch every corpus, then cargo test --release --features corpus on the corpus
-                  crates; --changed runs only if psd/io/codecs/compose/gpu/text/format changed;
+                  crates; --changed runs only if psd/io/codecs/compose/gpu/text/format/raw changed;
+                  --pixls (or -p raw) also fetches corpus/pixls and runs the raw corpus tests;
                   --local takes corpus/photoshop from the photocraft-corpus authoring clone
   stats [--exact] count tests and lines per crate (--exact: ask the test harness via `-- --list`)
   parity          Photoshop menu parity; rewrites docs/parity.md