fix: Enable DESTRUCTOR_CLOSES_FILE flag (#1075)

## Summary

* Enable `DESTRUCTOR_CLOSES_FILE` flag
* We're never intending to not close files, so if we accidentally leave
them open as they're destructured, this will help close them.

## Additional Context

* As spotted in
https://github.com/crosspoint-reader/crosspoint-reader/pull/869, there
are cases where we were accidentally not closing files

Looks to use about 5K of flash.

```
RAM:   [===       ]  31.5% (used 103100 bytes from 327680 bytes)
Flash: [=======   ]  68.9% (used 4513220 bytes from 6553600 bytes)
```

```
RAM:   [===       ]  31.5% (used 103100 bytes from 327680 bytes)
Flash: [=======   ]  68.9% (used 4518498 bytes from 6553600 bytes)
```


---

### AI Usage

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Did you use AI tools to help write this code? No

platformio.ini

@@ -24,6 +24,7 @@ build_flags =
   -DARDUINO_USB_CDC_ON_BOOT=1
   -DEINK_DISPLAY_SINGLE_BUFFER_MODE=1
   -DDISABLE_FS_H_WARNING=1
+  -DDESTRUCTOR_CLOSES_FILE=1
 # https://libexpat.github.io/doc/api/latest/#XML_GE
   -DXML_GE=0
   -DXML_CONTEXT_BYTES=1024