What’s new in Git 2.51.0?

Git 2.51.0 introduces performance optimizations for `git-push` and `git-fetch` by using batched reference updates instead of separate transactions, leading to significant speed improvements, especially for repositories with many references. This change improves the performance of the 'reftable' backend, making it outperform the 'files' backend. The release also marks the transition to 'reftable' as the default reference backend for new repositories and wires up SHA-256 as the default hash function for Git 3.0. The deprecated `git-whatchanged(1)` command is marked for removal in Git 3.0, and `git switch` and `git restore` are no longer experimental.