Add diff-driver command for semantic lockfile diffs and related tests

[andrew]

Install a git textconv driver that shows semantic dependency changes instead of raw lockfile diffs:

git pkgs diff-driver --install

Now git diff on lockfiles shows a sorted dependency list instead of raw lockfile changes:

diff --git a/Gemfile.lock b/Gemfile.lock
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,3 +1,3 @@
+kamal 1.0.0
-puma 5.0.0
+puma 6.0.0
 rails 7.0.0
-sidekiq 6.0.0

Use git diff --no-textconv to see the raw lockfile diff. To remove: git pkgs diff-driver --uninstall