pyfocs_calibration_check bath validation

```
f = pyfocs.bath_validation(
    ds_calibrated,
    cfg['calibration']['library'],
    fig_kwargs={'figsize': (9, 8)},
    temp_field_name='cal_temp')
```
Plotting does not work
UFuncTypeError: Cannot cast ufunc 'greater_equal' input 0 from dtype('<m8[ns]') to dtype('<m8') with casting rule 'same_kind'