Support local git diff with bun.lockb

This is following the Bun [guide][1]/[docs][2] for enabling git diffs
for `bun.lockb`

This won't work on GitHub, and this file isn't currently checked into
git. It is supported by Renovate, so we could check it in, but there are
various issues with this including [increased merge conflicts with
dependency management][3] and [potential security threats][4]. This
issue should be resolved and this change revertible when [Bun moves to a
by-default text-based lockfile][5] and Renovate adds support

[1]: https://bun.sh/guides/install/git-diff-bun-lockfile
[2]: https://bun.sh/docs/install/lockfile#how-do-i-git-diff-bun-s-lockfile
[3]: oven-sh/bun#5486
[4]: oven-sh/bun#5486 (comment)
[5]: oven-sh/bun#11863

.gitattributes

@@ -0,0 +1 @@
+*.lockb binary diff=lockb

.gitconfig

@@ -0,0 +1,3 @@
+[diff "lockb"]
+	textconv = bun
+	binary = true