Fix server rebuilds when adding sub sections especially on Windows

This commit also optimizes for the case where change events for both file (e.g. `_index.md`) and the container directory comes in the same event batch.

While testing this on Windows 11 (ARM64), I notice that Windows behaves a little oddly when dumping a folder of files into the content tree; it works (at least after this commit), but it seems like the event batching behaves differently compared to other OSes (even older Win versions).

A related tip would be to try starting the server with polling, to see if that improves the situation, e.g.:

```
hugo server --poll 700ms
```

Fixes #12230

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