Remove the `{D}` format specifier. It is moved into `std.Io.Duration` as
a format method.

Migration plan:

```diff
-writer.print("{D}", .{ns});
+writer.print("{f}", .{std.Io.Duration{ .nanoseconds = ns }});
```

All instances where `{D}` was used have been changed to use
`std.Io.Duration` and `{f}`.

Fixes #31281