GeezerVison

This may indicate accidental data loss.

Ways to make sure all data is written:
1. Use the [file-like object](https://docs.python.org/3/glossary.html#term-file-object) as a [“With Statement Context Manager”](https://docs.python.org/3/reference/datamodel.html#context-managers).
   - All objects which [inherit](https://docs.python.org/3/tutorial/classes.html#inheritance) from [IOBase](https://docs.python.org/3/library/io.html#io.IOBase) support this.
   - [`BufferedIOBase`](https://docs.python.org/3/library/io.html#io.BufferedIOBase), [`BufferedWriter`](https://docs.python.org/3/library/io.html#io.BufferedWriter), and [`GzipFile`](https://docs.python.org/3/library/gzip.html#gzip.GzipFile) all support this.
   - Ensures `.close()` is called in both exception and regular cases.
1. Ensure [`.close()`](https://docs.python.org/3/library/io.html#io.IOBase.close) is always called which flushes data before closing.
1. If the underlying stream need to be kept open, use [`.detach()`](https://docs.python.org/3/library/io.html#io.BufferedIOBase.detach)

Since 3.12 flushing has been necessary in GzipFile (see pythongh-105808 which was a release blocker), this makes that more visible. Users have been encountering as they upgrade to 3.12 (ex. pythongh-129726).

There are a number of cases of unclosed file-like objects being deleted in CPython libraries and the test suite. This issue includes resolving those cases where the new ResourceWarning is emitted.

Co-authored-by: Victor Stinner <[email protected]>

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