CVE-2020-35916: Mutable reference with immutable provenance in image

The vulnerability stems from macro-generated Pixel trait implementations using slice::as_ptr() instead of slice::as_mut_ptr() in their from_slice_mut functions. The commit diff shows the fix was applied to a macro template in src/color.rs that generates these pixel type implementations. The RustSec advisory explicitly lists these functions as vulnerable, and the CVE description confirms the pattern of creating mutable references from pointers with immutable provenance. High confidence comes from: 1) Direct match between patched code and vulnerable functions 2) Explicit listing in advisory 3) Clear explanation in commit message about pointer provenance violation.