refactor(prt): use enums for particle status and events

[wpbonelli]

Use enums for particle status and event codes, following #2188. Also remove an unnecessary/incorrect termination condition left over from #2185 in the base MethodType%check() routine — stationary particles get terminated at the end of the simulation by the tracking loop with timeout status, previously status 5 (no exit face) was getting reported.

Re: event code naming, I wonder if instead of "ireason", "ievent" might be clearer. The "reason" we're reporting in general is because an event of interest has occurred.. But this would change output headers so maybe best to wait for a non-bugfix release, if any change is to be made.

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Checklist of items for pull request

• Replaced section above with description of pull request
• Following refactor(gwt-mst): apply enumeration to mst package for readability #2188
• Added new test or modified an existing test
• Formatted new and modified Fortran source files with fprettify
• Added doxygen comments to new and modified procedures
• Removed checklist items not relevant to this pull request

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