[Bug]: QFDataArray Missing __slots__ Definition

[myrmarachne]

Environment

- QF-Lib: 4.0.4
- Python: 3.11.9

What happened?

When running multiple chart scripts (e.g., annual_returns_bar_chart.py, bar_chart_demo.py, cone_chart.py, etc.), a FutureWarning is displayed:

qf-lib\qf_lib\containers\qf_data_array.py:30: FutureWarning: xarray subclass QFDataArray should explicitly define __slots__
  class QFDataArray(xr.DataArray):

This warning appears in almost all chart scripts that use QFDataArray.

Screenshots

![DESCRIPTION](LINK.png)

Reproduction steps

1. Navigate to the `demo_scripts/charts` directory
2. Run any chart script that uses QFDataArray, for example: `python annual_returns_bar_chart.py`
3. Observe the FutureWarning in the console output

Relevant log output