Change method: statistic from Property to Method to allow eg active.mean(axis=(0, 1)) and instriduce comprehensive testing of Reductionist axis implementation

[valeriupredoi]

A bit of a lengthy one, but in a nutshell:

• eg a stat mean is not a property anymore, but a method, so active.mean[...] becomes active.mean()[...] so we can pass args and kwargs, so now you can active.mean(axis=(0, 1))[...]
• add plenty of testing for Reductionist's new axis - which currently doesn't work as expected, see below

Main test case for Reductionist with axis

https://github.com/NCAS-CMS/PyActiveStorage/blob/axis_api/tests/test_real_s3_with_axes.py

• Active loads a 4dim dataset
• Loaded dataset <HDF5 dataset "m01s30i111": shape (120, 85, 324, 432), type "float32">
• default axis arg (when axis=None): 'axis': (0, 1, 2, 3)

Test Case 1

def test_no_axis_2():
    """
    Fails: it should pass: 'axis': (0, 1, 2, 3) default
    are fine!

    activestorage.reductionist.ReductionistError: Reductionist error: HTTP 400: {"error": {"message": "request data is not valid", "caused_by": ["__all__: Validation error: Number of reduction axes must be less than length of shape - to reduce over all axes omit the axis field completely [{}]"]}}
    """
    active = build_active()
    result = active.min(axis=())[:]
    assert result == [[[[164.8125]]]]

Test Case 2

def test_axis_0_1():
    """Fails: activestorage.reductionist.ReductionistError: Reductionist error: HTTP 502: -"""
    active = build_active()
    result = active.min(axis=(0, 1))[:]
    assert result == [[[[164.8125]]]]

Test Case 3

def test_axis_0_1_2():
    """Passes fine."""
    active = build_active()
    result = active.min(axis=(0, 1, 2))[:]
    assert result[0][0][0][0] == 171.05126953125

These fails are here https://github.com/NCAS-CMS/PyActiveStorage/actions/runs/20272446127/job/58211728980?pr=300