chore(main): release 1.2.0

[github-actions]

🤖 I have created a release beep boop

1.2.0 (2026-09-30)

Features

• lift the PNG pixel stage to decode_png, and prove the one-block PNG round trip (#64) (56a42da)
• prove IMG-JPG-2, the JPEG planes from Array.set to decode_jpeg's pixels (#67) (75c266c)
• prove IMG-PNG-3 and IMG-PNG-4, the PNG encoder's refusals and IHDR (#56) (94e3312)
• prove IMG-RAS-1 to IMG-RAS-4, the raster helpers (#58) (3bd0909)
• prove the PNG round trip (IMG-PNG-2), and IMG-PNG-9 and IMG-PIX-1 with ancillary chunks (#69) (316f3ef)

Bug Fixes

• exact T.871 colour conversion in JPEG decode; settle IMG-JPG-2, IMG-JPG-3 and IMG-JPG-6 (#61) (f452c29)

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[github-actions]

🤖 Created releases:

• v1.2.0

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