Have to disable rescaling with monkey patching...

As pointed out in [Debian bugs #1063943] and [then #1071794],
test/test_cli.py fails with pytest 8 and beyon with the following
symptoms:

	__________________________ TestDcmstackCli.test_basic __________________________

	self = <test.test_cli.TestDcmstackCli object at 0x7f2d3a00eb40>

	    def test_basic(self):
	>       nii_paths = make_niftis(self.out_dir)
	E       AttributeError: 'TestDcmstackCli' object has no attribute 'out_dir'

	test/test_cli.py:55: AttributeError
	__________________________ TestDcmstackCli.test_embed __________________________

	self = <test.test_cli.TestDcmstackCli object at 0x7f2d3c976180>

	    def test_embed(self):
	>       nii_paths = make_niftis(self.out_dir, ['--embed'])
	E       AttributeError: 'TestDcmstackCli' object has no attribute 'out_dir'

	test/test_cli.py:59: AttributeError
	___________________________ TestNitoolCli.test_basic ___________________________

	self = <test.test_cli.TestNitoolCli object at 0x7f2d39f5b1d0>

	    def test_basic(self):
	>       nii_path = make_niftis(self.out_dir, ['--embed'])[0]
	E       AttributeError: 'TestNitoolCli' object has no attribute 'out_dir'

	test/test_cli.py:65: AttributeError

This is because pytest 8 deprecated the use of plain _setup_ and
_teardown_, which were compatibility layers to ease the porting effort
from Nose.  This change ensures methods inheriting from CliTest get
set up and teared down properly.

[Debian bugs #1063943]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1063943
[then #1071794]: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1071794

Signed-off-by: Étienne Mollier <emollier@debian.org>

t/test_cli.py: port setup/teardown to pytest 8.

prefer newer unittest.mock from standard library

Have to disable rescaling with monkey patching...

…-multiframe