Control tolerance for assert_frame_equal

[cwhanse]

It would be nice to be able to supply atol and/or rtol to pvlib.conftest.assert_frame_equal.

For any pandas > 1.1, current behavior sets either atol, rtol = [1e-3, 1e-3] or atol, rtol = [1e-5, 1e-5]. If atol or rtol are specified they are silently ignored.

Describe the solution you'd like
Pass atol and rtol through to pd.testing.assert_frame_equal

Describe alternatives you've considered
Live with it and compute more accurate test solutions.

[wholmgren]

NEP-29 says we can increase the minimum pandas to 1.1 and get rid of the test silliness.