warn or raise error when merge/wrap inconsistent axes

[ykyohei]

Now I think this was probably intended behavior, but merge and wrap always silently intersect and restrict axes.
Added an on_mismatch to warn or raise error when the coverage of axes with same name are different.

This silent intesection/truncation caused issues in analysis several times, for example when we calculate psd with different length of trimmed data, or after downsampling.
We need to rename axes in such cases but I think default warning (or error) is helpful..

Example:

WARNING: sotodlib.core.axisman: Axis mismatch on merge/wrap causes truncation: axis 'dets' of self changes LabelAxis(3:np.str_('det0'),np.str_('det1'),np.str_('det2')) -> LabelAxis(2:np.str_('det0'),np.str_('det1')).
WARNING: sotodlib.core.axisman: Axis mismatch on merge/wrap causes truncation: axis 'samps' of self changes OffsetAxis(1000:None+0) -> OffsetAxis(900:None+0).