Release 0.7.5 with published Burn adapter

[jcwal1516]

What changed

• bumps the workspace and all exact internal dependencies to 0.7.5
• publishes j2k-ml as the 19th release crate with CPU, CUDA, and Metal Burn integration
• records the reviewed j2k-ml public API and 0.7.5 compatibility exception
• finalizes changelog, release documentation, and patched-dependency approvals

Validation

• focused j2k-ml release-policy regressions
• cargo check -p j2k-ml --features cpu
• cargo clippy -p xtask --all-targets -- -D warnings
• cargo xtask fmt
• cargo xtask repo-lint --strict
• cargo xtask release-integrity --publish
• cargo xtask package

Runtime and accelerator source is unchanged by this release-preparation branch. Exact-SHA hosted, Metal, and CUDA release evidence will run once after merge.