TST: split tests for windows to sub-modules

[jreback]

after #18723

can split test_window.py to a sub-dir pandas/tests/window/ and have
test_rolling, expanding, emwa and prob test_window (for other)

[sunilk747]

@jreback Hello. I am new to pandas repo. I would really like to work on this issue. Can you please provide more details regarding what are the things to be done here.

[jreback]

we need to split test_window.py to 3 files in a subdir window

test_rolling
test_expanding
test_ewma

[giba0]

Hello @sunilk747 Are you still working on it?

[sunilk747]

@gilbertoolimpio No. I am not working on it. If you want to take up this issue please go ahead.

[giba0]

OK! @sunilk747 I will work on it!