* use `os.CreateTemp` in `tempfile.CreateAutoDelete`
* refactor `TestTempFile`: add `VerifyTempfile` test helper
* add test for `createUnixFallback`
* rename function to `tempfile.CreateAutoDelete`
* remove the `dir` parameter to `tempfile.CreateAutoDelete`,
only an empty string was passed, apart from test cases.
* guard against panic in TestShadowCopy