"prune" materializer task

[sandreae]

Introduces a "prune" materialization task which:

• is issued whenever a "reduce" task completes when the input was a DocumentId (this is a new current view)
• the "prune" task looks at the updated document and deletes any rows from the document_views and document_view_fields table where: they are not the current view AND they are not targeted from a pinned relation of any other document

I also had to make some changes to prune_document_views method which was introduced onto the store in a previous PR cos it was not doing what it's supposed to....

📋 Checklist

• Add tests that cover your changes
• Add this PR to the Unreleased section in CHANGELOG.md
• Link this PR to any issues it closes
• New files contain a SPDX license header

[codecov]

Codecov Report

Patch coverage: 97.55% and project coverage change: +0.99% 🎉

Comparison is base (81cae95) 91.20% compared to head (0a93f68) 92.20%.

❗ Current head 0a93f68 differs from pull request most recent head 8c7938f. Consider uploading reports for the commit 8c7938f to get more accurate results

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #496      +/-   ##
===============================================
+ Coverage        91.20%   92.20%   +0.99%     
===============================================
  Files              101      102       +1     
  Lines            16393    16644     +251     
===============================================
+ Hits             14952    15347     +395     
+ Misses            1441     1297     -144     

Files Changed	Coverage Δ
aquadoggo/src/materializer/tasks/reduce.rs	95.04% <86.20%> (-0.24%)	⬇️
aquadoggo/src/test_utils/node.rs	92.51% <96.61%> (-2.32%)	⬇️
aquadoggo/src/materializer/tasks/prune.rs	98.07% <98.07%> (ø)
aquadoggo/src/db/stores/document.rs	98.74% <99.00%> (+12.93%)	⬆️
aquadoggo/src/materializer/service.rs	94.76% <100.00%> (+0.01%)	⬆️
aquadoggo/src/materializer/tasks/dependency.rs	97.54% <100.00%> (+<0.01%)	⬆️

... and 3 files with indirect coverage changes

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[sandreae]

This work is being continued in a new branch here: #500