[mpgopala]

Changes in this pull request

Update to_c_bytes to hand off the original Rust Vec<u8> allocation to C when its address is even, eliminating the intermediate allocation and copy.

• Preserve the original pointer, length, and capacity without shrinking or copying to reduce spare capacity.
• Reconstruct and drop the original vector only when registry cleanup runs.
• Preserve cancellation semantics: dropping a cancelled cleanup closure does not free the transferred allocation.
• Retain the aligned-copy fallback for odd-addressed allocations, as required by the registry’s pointer-tagging scheme.
• Preserve empty-buffer behavior, error reporting, and existing release conventions.
• Update ownership documentation and the changelog.

No public API or C ABI changes. Callers continue to treat returned bytes as read-only and release them through the existing library cleanup mechanism.

Validation

The following commands passed against the cimpl manifest:

• cargo test --manifest-path /Users/gsharma/source/c2pa/cimpl/Cargo.toml — 61 tests passed; 27 documentation examples ignored.
• cargo clippy --manifest-path /Users/gsharma/source/c2pa/cimpl/Cargo.toml --all-targets -- -D warnings — passed.
• cargo fmt --manifest-path /Users/gsharma/source/c2pa/cimpl/Cargo.toml --check — passed.
• cargo +nightly miri test --manifest-path /Users/gsharma/source/c2pa/cimpl/Cargo.toml --lib to_c_bytes — 8 tests passed.

Regression coverage includes allocation identity, retained spare capacity, odd-address fallback, empty inputs, tracking refusal, cancellation, cross-thread release, double-free rejection, and untracked pointers.

Miri exercised genuine odd-addressed allocations. It emits exposed-provenance warnings for pointer reconstruction, so these results are not a strict-provenance proof.

No crate version bump or publication is included.

Checklist

• This PR represents a single feature, fix, or change.
• All applicable changes have been documented.
• Any TO DO items (or similar) have been entered as GitHub issues and the link to that issue has been included in a comment.