Add `Kind::empty_blob()` and `Kind::empty_tree()` methods to gix-hash#2165

Byron merged 2 commits intomainGitoxideLabs/gitoxide:mainfrom

copilot/fix-ceb7b1a4-93f5-4da1-a4f2-4290c8f594ebGitoxideLabs/gitoxide:copilot/fix-ceb7b1a4-93f5-4da1-a4f2-4290c8f594ebCopy head branch name to clipboard