[Feature]: Optimize postprocessing_E3SM_data_for_single_sites.py to improve to_netcdf() performance

[tomvothecoder]

Is your feature request related to a problem?

In PR #907, postprocess_E3SM_data_for_single_sites.py was refactored to resolve chunking issues related to time_bounds. In the process, the script was re-written to replace CDAT with Xarray/xCDAT. The script works and was tested with v3 data, but the to_netcdf() performance is slow.

Describe the solution you'd like

• Find areas of code to refactor
• Optimize to_netcdf() performance

Describe alternatives you've considered

No response

Additional context

No response