Sum over fine energy bins by default

[grazwegian]

When the energy bins are fine the proportional discrepancy introduced by the ELUT can be significant. During the fine bin campaign 2023-07-31 to 2023-11-04 three energy bins between 6.3 and 7.3 keV were determined (6.3 - 6.56, 6.56 - 6.8. and 6.8- 7.3) to better investigate the Iron and Nickel lines in this region. For more standard spectroscopy to minimise the ELUT correction error it is more convenient to combine these bins into a single 6.3 - 7.3 bin. This would be the default mode for the stx_convert routines with the full energy resolution data being available through a keyword.