Fixturize tests/frame/test_arithmetic
Split off from #22730 as per review from @WillAyd 

The changes in `conftest.py` are due to the following:
> In translating the quasi-fixtures from `TestData` to `conftest` in #22236, I sorted the dtypes for the columns of `mixed_float_frame` and `mixed_int_frame`, which turns out to have been a mistake. This is reverted here to be a true translation of the attribute of `TestData`. Otherwise, tests in the newly fixturized `test_arithmetic.py` would fail.