Fix: dedup generated schema fields by key

[sandreae]

Fixes a logic error in the proptests which was causing intermittent test failures. And a refactor so test regressions go into named files per test.

closes: #520 #459

📋 Checklist

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

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (6b13189) 92.45% compared to head (ebb7274) 92.46%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #558 +/- ## ======================================= Coverage 92.45% 92.46% ======================================= Files 106 106 Lines 18039 18039 ======================================= + Hits 16678 16679 +1 + Misses 1361 1360 -1 ``` [see 1 file with indirect coverage changes](https://app.codecov.io/gh/p2panda/aquadoggo/pull/558/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=p2panda)

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