suppress chunking warning again

[veenstrajelmer]

chunking warning was suppressed in #679, then suppression was reverted in #888.

However, the below code still raises the performancewarning:

import dfm_tools as dfmt
file_nc = r'p:\11208983-epd-support-tools\toolbox\EPD_Support_Tool\simulations\HK-DFM_scenario\DFM_OUTPUT_HK-FMWAQ\HK-FMWAQ_0000_map.nc'
uds = dfmt.open_partitioned_dataset(file_nc)

Prints:

>> xu.open_dataset() with 1 partition(s): 1 C:\Users\veenstra\Anaconda3\envs\dfm_tools_env\Lib\site-packages\xarray\core\dataset.py:274: UserWarning: The specified chunks separate the stored chunks along dimension "time" starting at index 1. This could degrade performance. Instead, consider rechunking after loading.
  warnings.warn(
: 0.36 sec

Apparently it still needs suppression for some files, so has to be suppressed again. Consider doing it in dfmt.open_partitioned_dataset() with a with-statement and maybe make it optional with a keyword.