Add FutureWarning for converting Series with NaN to bool dtype

[mzarnecki]

Related to #62687

This PR adds a FutureWarning when using astype() to convert data containing NaN values to bool dtype. In pandas 3.0, this will raise a ValueError instead.

Changes:

• Added warning in _astype_nansafe() that triggers when converting to np.bool_ with NaN present
• Added test test_astype_bool_with_nan_warning() to verify the warning behavior
• Updated doc/source/whatsnew/v2.3.4.rst

Example:

ser = pd.Series([1.0, 2.0, np.nan])
ser.astype(bool)  # FutureWarning: Converting a Series with NaN values to bool...