Fix UserWarning with development numpy version

[mscheltienne]

With the development version of numpy 2.4.0.dev0, we get:

.venv/lib/python3.13/site-packages/pyxdf/pyxdf.py:362: in load_xdf
    temp = _clock_sync(
.venv/lib/python3.13/site-packages/pyxdf/pyxdf.py:674: in _clock_sync
    _coefs = _robust_fit(X, y)
             ^^^^^^^^^^^^^^^^^
.venv/lib/python3.13/site-packages/pyxdf/pyxdf.py:824: in _robust_fit
    d_inv = np.divide(1, d, where=d != 0)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E   UserWarning: 'where' used without 'out', expect unitialized memory in output. If this is intentional, use out=None.

This PR should fix this by pre-allocating a zero array and then writing the results in this pre-allocated array.

[cbrnr]

Thanks! Do you want to add a changelog entry?

[mscheltienne]

Done!

[cbrnr]

Thanks @mscheltienne!