Allow visit completion to run more asynchronously

[d-j-hatton]

The multigrid controller should now be able to handle most of the process of cleaning up all associated threads. Thread completion requests are performed by setting flags and not explicitly waiting for joins. Callbacks are then used to notify of thread completion. (RSyncer threads are slightly more complicated because they have to perform file removal after completing.)

On completion of all associated threads the multigrid controller will mark itself as dormant. When new multigrid controllers are added dormant controllers are checked for and removed along with the associated Murfey session data. This could also possibly be triggered when the controller marks itself as dormant for a quicker cleanup?

[codecov]

Codecov Report

Attention: Patch coverage is 17.64706% with 56 lines in your changes missing coverage. Please review.

Project coverage is 29.93%. Comparing base (28a47f7) to head (3c44eb9).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #543      +/-   ##
==========================================
+ Coverage   28.97%   29.93%   +0.96%     
==========================================
  Files          80       80              
  Lines       10309    10907     +598     
  Branches     1363     1450      +87     
==========================================
+ Hits         2987     3265     +278     
- Misses       7221     7533     +312     
- Partials      101      109       +8     

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[d-j-hatton]

Attempts to resolve #530

[d-j-hatton]

Need to check that controller is dormant before deleting session from database

[tieneupin]

Some suggestions, but other than that, no obvious errors! 👍