jxl-oxide: Out-of-bounds writes due to integer overflow in jxl-grid on 32-bit platforms

Summary

jxl-oxide is a pure Rust implementation of a JPEG XL decoder. Prior to jxl-grid 0.6.2, decoding a crafted JPEG XL image on a 32-bit platform can overflow length calculations in AlignedGrid::with_alloc_tracker and related grid and subgrid arithmetic. A 65536 x 65536 frame can pass the frame-area limit while overflowing the usize element count, causing modular, VarDCT, or filter rendering paths to allocate a backing buffer smaller than the logical grid. A tiny bitstream-controlled cropped frame combined with a huge canvas or requested region can also reach the vulnerable composition path in crates/jxl-render/src/blend.rs through ordinary render_frame(). Later mutable subgrid and raw-pointer operations can then perform attacker-controlled out-of-bounds writes, causing memory corruption, denial of service, or arbitrary code execution. This issue is fixed in jxl-grid version 0.6.2.