LoadEventNexus change tofmin to be at the lowest event's tof

[peterfpeterson]

Since histogramming is inclusive on the lower bound, there is need to shift the lower boundary to the left. The effect of the current implementation is that when the smallest TOF is <1, the workspace histogram started at negative values which makes a mess for log (re)binning.

There is no associated issue, but this is tracked with EWM6796

To test:

This was originally seen with SNAP_61408, but load any event file where the minimum time-of-flight is between zero and one. After using LoadEventNexus, view the data and see what the minimum x-value is using the "show data" visualization. Also note that the logs will say something like

LoadEventNexus-[Information] Read 1677139 events. Shortest TOF: 0.7 microsec; longest TOF: 16666.6 microsec.

before this change, the minimum bin boundary will be -0.3 micorseconds; after this change it will be 0.7 microseconds.

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[sf1919]

It looks like the failing tests for linux might be genuine now so I will not re-run the tests on this one.

[peterfpeterson]

Thanks for looking into this. There are indeed 4 failing system tests and it is just taking me time to get back to this and fix them.

[dlcaballero16]

Tested LoadEventNexus with SNAP 61408 and was able to confirm X values were no longer starting with negative numbers.