Make value on QueryRow an option

[sandreae]

📋 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: 100.00% and project coverage change: +0.26 🎉

Comparison is base (784a0ef) 89.46% compared to head (49938fa) 89.72%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #339      +/-   ##
==========================================
+ Coverage   89.46%   89.72%   +0.26%     
==========================================
  Files          70       70              
  Lines        5998     6093      +95     
==========================================
+ Hits         5366     5467     +101     
+ Misses        632      626       -6     

Impacted Files	Coverage Δ
aquadoggo/src/db/models/query.rs	100.00% <ø> (ø)
aquadoggo/src/db/stores/query.rs	94.68% <100.00%> (+0.41%)	⬆️
aquadoggo/src/graphql/queries/all_documents.rs	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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