One would assume that this class implements the IOBase abstract. As the
underlying file-like object is either io.BytesIO, io.StringIO, or a true
file object, this is a reasonable abstract expect and to implement.

Regardless, the behaviour of this class does not change much in the case
of the attribute being missing from the underlying file-like; an
AttributeError is still raised, albeit from one additional frame on the
stack trace.

Part of file interface:
https://docs.python.org/library/io.html#io.IOBase.seek

We don't want to delete the underlying file explicitly as the expected
behaviour is for the file to be deleted *after* it falls out of scope.

Part of file interface:
https://docs.python.org/library/io.html#io.IOBase.truncate

…edTemporaryFile-IOBase

Co-Authored-By: Éric Araujo <[email protected]>

This reverts commit b588dec.

The underlying file should be deleted when the SpooledTemporaryFile
object is deleted. This follows the same behaviour as TemporaryFile and
is consistent with the documentation. `__del__` should have the same
consequences as using `del` or allowing the object to fall out of scope;
an expectation which b588dec (reverted) broke somewhat.