NEP29 for Release 1.6

[mrfh92]

According to the standard described in https://numpy.org/neps/nep-0029-deprecation_policy.html we...

• definitely should add sth with NumPy 2.x
• should support Python 3.13 as PyTorch 2.6.0 (see Support PyTorch 2.6.0 / Add zarr as optional dependency  #1775) seems to support it
• can drop Python<=3.11 in April 2026
• certainly can drop some old PyTorch versions as well