ValueError: No engine for filetype: 'xls'

[cefect]

looks like the default xls engine is no longer supported by Qgis. see tests2.tutorials.test_t2.test_t2_A.

Traceback (most recent call last):
  File "c:\OSGeo4W\apps\Python312\lib\site-packages\pandas\io\excel\_base.py", line 1136, in __new__
    engine = config.get_option(f"io.excel.{ext}.writer", silent=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "c:\OSGeo4W\apps\Python312\lib\site-packages\pandas\_config\config.py", line 274, in __call__
    return self.__func__(*args, **kwds)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "c:\OSGeo4W\apps\Python312\lib\site-packages\pandas\_config\config.py", line 146, in _get_option
    key = _get_single_key(pat, silent)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "c:\OSGeo4W\apps\Python312\lib\site-packages\pandas\_config\config.py", line 132, in _get_single_key
    raise OptionError(f"No such keys(s): {repr(pat)}")
pandas._config.config.OptionError: No such keys(s): 'io.excel.xls.writer'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "L:\09_REPOS\04_TOOLS\CanFlood\canflood\build\dialog.py", line 790, in purge_curves
    curves_fp_clean = wrkr.output(cLib_d)
                      ^^^^^^^^^^^^^^^^^^^
  File "L:\09_REPOS\04_TOOLS\CanFlood\canflood\misc\curvePlot.py", line 515, in output
    with pd.ExcelWriter(ofp) as writer:
         ^^^^^^^^^^^^^^^^^^^
  File "c:\OSGeo4W\apps\Python312\lib\site-packages\pandas\io\excel\_base.py", line 1140, in __new__
    raise ValueError(f"No engine for filetype: '{ext}'") from err
ValueError: No engine for filetype: 'xls'

1. try other engines to see if these work in QGIS
2. if no engines work on the default QGIS, add a new dependency.

[cefect]

fixed with PR #109.
However, it would be nice to upgrade everything to support .xlsx in the future (need to continue to support .xls for backwards compatability)