git: Add attempt at migrating to delta

This was my attempt at migrating from diff-so-fancy to delta. Although
having an easy-to-hack-on rust code base was certainly appealing, there
are some minor inconveniences such as longer diffs by default.

home/git.nix

@@ -53,6 +53,13 @@
       };
     };
 
-    diff-so-fancy.enable = true;
+    delta = {
+      enable = true;
+      options = {
+        diff-so-fancy = true;
+        hunk-header-style = "file line-number syntax";
+        hunk-header-decoration-style = "none";
+      };
+    };
   };
 }