Refactoring #cellDiscarded message creation and reception

[darth-cheney]

This PR restructures the way cellDiscarded (now cellsDiscarded) messages are composed, received, and ultimately handled on the Component side. This is in relation to #104

Motivation and Context

See Issue #104 for details. We were sending (potentially) too many messages for discarding cells per rendering cycle

Approach

Instead of composing a single message per Cell being discarded, we now send over an array of all ids of cells to be discarded at the same time.

The CellHandler has also been updated to deal with this change.

We have changed all references to cellDiscarded and renamed them cellsDiscarded

How Has This Been Tested?

All existing tests are passing as normal

Screenshots or console output (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #105 into dev will decrease coverage by 0%.
The diff coverage is 100%.

@@         Coverage Diff         @@
##            dev   #105   +/-   ##
===================================
- Coverage    62%    62%   -1%     
===================================
  Files        86     86           
  Lines      9090   9095    +5     
===================================
- Hits       5693   5659   -34     
- Misses     3397   3436   +39     

Impacted Files	Coverage Δ
object_database/web/cells/Messenger.py	89% <100%> (-2%)	⬇️
object_database/web/cells/cells.py	54% <100%> (+<1%)	⬆️
object_database/service_manager/Task.py	28% <0%> (-23%)	⬇️
object_database/database_connection.py	90% <0%> (+<1%)	⬆️
object_database/tcp_server.py	92% <0%> (+<1%)	⬆️
object_database/service_manager/ServiceBase.py	94% <0%> (+30%)	⬆️

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[darth-cheney]

@braxtonmckee LMK if you are good to merge this. Would be useful to have for some ongoing work I'm doing. Should save a lot of bits going over the wire.