Git 2.56 makes conflict staging and merge-base walks safer

Git 2.56 adds git add --resolved, which stages only paths involved in a merge conflict and refuses to proceed when selected files still contain conflict markers.

The release also improves merge-base traversal, with reported large speedups in some monorepo and Linux-kernel cases.

Path-walk repacks can now use reachability bitmaps and delta islands, removing two barriers to evaluating their storage savings on repository hosts.