chore: remove old and unused code

highlight_test.go

@@ -106,3 +106,17 @@ func TestHighlightDiffRemovesOnlyCommonIndent(t *testing.T) {
 		t.Fatalf("dedented code:\n%q\nwant:\n%q", got, want)
 	}
 }
+
+func TestHighlightDiffCacheReturnsIndependentSlices(t *testing.T) {
+	highlightedDiffs.clear()
+
+	first := highlightDiff("main.go", "@@ -1 +1 @@\n-old\n+new", 1, 1, "RIGHT")
+	if len(first) == 0 {
+		t.Fatal("highlighted diff is empty")
+	}
+	first[0].code = "mutated"
+	second := highlightDiff("main.go", "@@ -1 +1 @@\n-old\n+new", 1, 1, "RIGHT")
+	if len(second) == 0 || second[0].code == "mutated" {
+		t.Fatalf("cached highlighted diff shares caller storage: %#v", second)
+	}
+}