Include all test files in sdist via MANIFEST.in

[VladimirGutuev]

Fixes #8159.

What's wrong

The sdist on PyPI for datasets==4.8.5 only ships 37 of the 95 files under tests/. Without an explicit MANIFEST.in, setuptools' default sdist behavior includes only top-level tests/test_*.py files and drops everything else.

Files missing from the current sdist:

• tests/conftest.py
• tests/_test_patching.py
• everything under tests/commands/, tests/features/, tests/fixtures/, tests/io/, tests/packaged_modules/, tests/distributed_scripts/
• the audio / image / PDF / JSON test-data files under tests/features/data/ and tests/io/data/

Anyone installing from sdist (distros, mirrors, air-gapped builds) cannot run the test suite — pytest fails to even collect because tests/conftest.py is missing the pytest_plugins configuration that pulls in tests.fixtures.*.

Fix

Add a minimal MANIFEST.in that grafts the whole tests/ directory and excludes bytecode.

graft tests
global-exclude __pycache__
global-exclude *.py[cod]

Verification

Built the sdist locally on main before/after the change and compared:

$ python -m build --sdist

	Before	After
Files under tests/ in sdist	37	95
tests/conftest.py	missing	included
tests/_test_patching.py	missing	included
tests/fixtures/fsspec.py	missing	included
tests/features/test_audio.py	missing	included
tests/io/test_csv.py	missing	included
tests/packaged_modules/test_arrow.py	missing	included
tests/features/data/test_audio_16000.mp3	missing	included
__pycache__ files	0	0

All 95 files under tests/ in the working tree are now in the sdist; nothing else is added.