Add support for dynamics crash reports

[lohedges]

This PR adds supports for saving crash reports during Sire dynamics runs using the save_crash_report kwarg when calling dynamics.run(). If specified, the following files will be saved during a crash:

• A log file with current lambda and energy contribution from each force.
• An XML file containing the OpenMM system.
• A NumPy text file containing the atomic positions.

All files correspond to the system at the start of the dynamics block, not the crash, which might not be available. This allows a user to replay a crash. Files are given a UUID name that is consistent across files, e.g. crash_UUID.log, system_UUID.xml, and positions_UUID.txt. I'm not sure whether we should allow the user to pass a name, or create the UUID for the dynamics object itself, then increment some file index, e.g. if there are multiple crashes along a trajectory. This probably isn't that important, since this is really intended to only be turned on when debugging unstable simulations to capture examples of soft-crashes. Happy to take suggestions, though.

• I confirm that I have merged the latest version of devel into this branch before issuing this pull request (e.g. by running git pull origin devel): [y]
• I confirm that I have added a test for any new functionality in this pull request: [y]
• I confirm that I have added documentation (e.g. a new tutorial page or detailed guide) for any new functionality in this pull request: [y]
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[mb2055]

All good 👍