fix(crate_universe): resolve escaping relative path deps during splicing

[0xbeefd1ed]

Splicing relocates the root Cargo manifest into a temporary workspace whose top-level entries are symlinks back into the source directory. Relative path dependencies that escape the manifest directory (e.g. ../sibling) therefore resolve against the temporary directory and fail with failed to read <tmp>/../sibling/Cargo.toml.

Anchor such dependencies to the original manifest directory before the spliced manifest is written:

• absolutize_escaping_path_deps rewrites a manifest's dependency, dev-dependency, build-dependency, target, workspace.dependencies and patch tables, absolutizing only paths that lexically leave the workspace root and leaving in-tree paths (and the package ids cargo metadata reports) untouched.
• absolutize_escaping_member_path_deps applies it to workspace members, which are reached through symlinks: for each member that needs a rewrite it materializes the symlinked ancestor directories into real directories (whose other entries link back to the source tree) and writes a rewritten copy of the member manifest, never modifying the source tree.

Adds unit coverage for the path-rewriting predicate and an end-to-end splice_workspace test that resolves an escaping member dependency via cargo metadata.

Assisted-by: Claude Opus 4.8

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.