findCargoLockfile doesn't follow package.workspace pointers #701

Problem

Cargo lets a crate name its workspace root explicitly with package.workspace = "<path>" instead of being found by walking up the directory tree. findCargoLockfile (packages/core/src/cargo.ts) only walks up, both on main and in #674's version, which otherwise follows cargo's root rule including exclude. So in a pointer layout:

• No own lock is found for the crate, and its lock isn't treated as its own.
• With fix(version)!: sync every committed Cargo.lock that records a bumped crate #674, the real root lock is still synced when another package in it depends on the crate. A pointer member that nothing depends on keeps a stale entry, and cargo metadata --locked then fails on that lock.

main has the same gap; #674 doesn't introduce it. The layout is rare.

Found during the #674 review (round 4). The reviewer compared findCargoLockfile against cargo metadata's workspace_root in 22 layouts, and this was the only mismatch.

Fix

In findCargoLockfile, read the crate's own package.workspace and, when set, use that directory as the root. It's a few lines on top of #674's TOML read. Add a core test pinned against cargo's choice. #674 notes the gap in the function's JSDoc; remove that note with the fix.