gix and gitoxide: unvalidated submodule name traverses out of .git/modules and redirects state() / open() to another repository

Summary attachments: pocs.zip Submodule names coming from .gitmodules are exposed as unvalidated names and are later reused to derive the submodule git directory as: /modules/ Because the submodule name is joined directly as a filesystem path component, a name such as ../../../escaped-target.git...