Generate a random name for in-memory database and set cache to shared by default

[adzialocha]

This is a fix around an issue with SQLite / sqlx https://github.com/launchbadge/sqlx/issues/2510 which corrupts our in-memory databases sometimes.

Closes https://github.com/p2panda/aquadoggo/issues/568

📋 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

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (efe445c) 92.75% compared to head (a27d312) 92.76%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #595 +/- ## ======================================= Coverage 92.75% 92.76% ======================================= Files 106 106 Lines 18558 18558 ======================================= + Hits 17214 17215 +1 + Misses 1344 1343 -1 ```

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