Fix the same problem in the std.Progress branch

Also added a test example for memory tracking to compare overhead.

build.zig

@@ -63,6 +63,7 @@ fn setupExamples(b: *std.Build, target: std.zig.CrossTarget, optimize: std.built
         "bubble_sort",
         "hooks",
         "json",
+        "memory_tracking",
         "parameterised",
         "progress",
         "sleep",

examples/memory_tracking.zig

@@ -0,0 +1,25 @@
+const std = @import("std");
+const zbench = @import("zbench");
+
+fn myBenchmark(allocator: std.mem.Allocator) void {
+    for (0..2000) |_| {
+        const buf = allocator.alloc(u8, 512) catch @panic("OOM");
+        defer allocator.free(buf);
+    }
+}
+
+test "bench test basic" {
+    const stdout = std.io.getStdOut().writer();
+    var bench = zbench.Benchmark.init(std.testing.allocator, .{
+        .iterations = 64,
+    });
+    defer bench.deinit();
+
+    try bench.add("My Benchmark 1", myBenchmark, .{});
+    try bench.add("My Benchmark 2", myBenchmark, .{
+        .track_allocations = true,
+    });
+
+    try stdout.writeAll("\n");
+    try bench.run(stdout);
+}

zbench.zig

@@ -243,10 +243,10 @@ pub const Benchmark = struct {
 
     /// Run all benchmarks using an iterator, collecting progress information
     /// incrementally.
-    pub fn iterator(self: Benchmark) !Iterator {
+    pub fn iterator(self: *const Benchmark) !Iterator {
         return Iterator{
             .allocator = self.allocator,
-            .b = &self,
+            .b = self,
             .remaining = self.benchmarks.items,
             .runner = null,
         };