Spine Items changes related to ditching Dagster

[ptsavol]

Re spine-tools/Spine-Toolbox#2523

Checklist before merging

• Documentation (also in Toolbox repo) is up-to-date
• Release notes in Toolbox repo have been updated
• Unit tests have been added/updated accordingly
• Code has been formatted by black
• Unit tests pass

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 61.74%. Comparing base (1ea1f1f) to head (1ec6075).

Files	Patch %	Lines
spine_items/db_writer_item_base.py	50.00%	1 Missing ⚠️
spine_items/exporter/exporter.py	50.00%	1 Missing ⚠️
spine_items/tool/tool.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           0.8-dev     #204      +/-   ##
===========================================
+ Coverage    61.71%   61.74%   +0.02%     
===========================================
  Files          190      190              
  Lines        17685    17687       +2     
  Branches      2897     2897              
===========================================
+ Hits         10914    10920       +6     
+ Misses        6187     6183       -4     
  Partials       584      584              

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