MuX: Improve Hexagons data file creation and management

# Feature Description
As a MuX instrument scientist I would like the creation and management of data files from the Hexagons to be robust and production worthy.

The MuX beamline currently creates a bare bones HDF5 with the event data, and a separate nxs file with the log data. Ideally this should be combined to a single nxs file with a standardised format.

## Explanation
Following on from #6109, we need to improve the processes around data management and file creation so they are more robust, maintainable and well documented.

### Additional Information
The Muon group are also looking at other acquisition technologies for this beamline, so work here may need to be coordinated with that plan (and an assessment made of the value of this work against that plan).

@FreddieAkeroyd is the current subject matter expert in the group.

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# Acceptance Criteria
- [ ] The MuX beamline produces a single nxs file containing all data in a standardised format
- [ ] This work, along with all work on generating files from the Hexagon digitisers is sufficiently documented to enable support

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