change test dir to top level

[stevenhua0320]

see scikit-package/scikit-package#114 for more details

[bobleesj]

@stevenhua0320 Could you also try to remove run.py and debug.py? They were used previously to collect and run unittest functions. Now pytest is used instead.

[stevenhua0320]

run via pytest
pytest
===================================================================== test session starts =====================================================================
platform darwin -- Python 3.12.4, pytest-7.4.4, pluggy-1.0.0
rootdir: /Users/huarundong/dbs/diffpy.srmise
collected 4 items

tests/test_dataclusters.py .... [100%]

====================================================================== 4 passed in 0.33s ======================================================================

[sbillinge]

please try and remove the tests/__init__.py