Support for pandas 3

[scw]

The current tests which rely on the pandas df structure fail because of changes in the data frame structure:

> pytest --pyargs slicer
============================= test session starts =============================
platform win32 -- Python 3.13.10, pytest-8.4.2, pluggy-1.5.0
collected 21 items

test_slicer.py ..F.F.........F..FF..                                     [100%]

=========================== short test summary info ===========================
FAILED test_slicer.py::test_slicer_unnamed - IndexError: too many indices for...
FAILED test_slicer.py::test_slicer_default_alias - AssertionError: assert None
FAILED test_slicer.py::test_slicer_pandas - IndexError: too many indices for ...
FAILED test_slicer.py::test_operations_1d - IndexError: too many indices for ...
FAILED test_slicer.py::test_operations_2d - IndexError: too many indices for ...
======================== 5 failed, 16 passed in 3.13s =========================