feat: Implement a prepare_connection plugin hook

[asg017]

Just like the Datasette prepare_connection hook, this PR adds a similar hook for the sqlite-utils plugin system.

The sole argument is conn, since I don't believe a database or datasette argument would be relevant here.

I want to do this so I can release sqlite-utils plugins for my SQLite extensions, similar to the Datasette plugins I've release for them.

An example plugin: https://gist.github.com/asg017/d7cdf0d56e2be87efda28cebee27fa3c

$ sqlite-utils install https://gist.github.com/asg017/d7cdf0d56e2be87efda28cebee27fa3c/archive/5f5ad549a40860787629c69ca120a08c32519e99.zip

$ sqlite-utils memory 'select hello("alex") as response'
[{"response": "Hello, alex!"}]

Refs:

• 574

---

:books: Documentation preview :books:: https://sqlite-utils--573.org.readthedocs.build/en/573/

[simonw]

I was literally seconds away from shipping version 3.34 but I this looks good so I'm going to try and get it in there.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03 :tada:

Comparison is base (86a352f) 96.09% compared to head (faf398f) 96.12%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #573 +/- ## ========================================== + Coverage 96.09% 96.12% +0.03% ========================================== Files 8 8 Lines 2794 2816 +22 ========================================== + Hits 2685 2707 +22 Misses 109 109 ``` | [Impacted Files](https://app.codecov.io/gh/simonw/sqlite-utils/pull/573?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Simon+Willison) | Coverage Δ | | |---|---|---| | [sqlite\_utils/\_\_init\_\_.py](https://app.codecov.io/gh/simonw/sqlite-utils/pull/573?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Simon+Willison#diff-c3FsaXRlX3V0aWxzL19faW5pdF9fLnB5) | `100.00% <100.00%> (ø)` | | | [sqlite\_utils/db.py](https://app.codecov.io/gh/simonw/sqlite-utils/pull/573?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Simon+Willison#diff-c3FsaXRlX3V0aWxzL2RiLnB5) | `97.36% <100.00%> (+0.01%)` | :arrow_up: | | [sqlite\_utils/hookspecs.py](https://app.codecov.io/gh/simonw/sqlite-utils/pull/573?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Simon+Willison#diff-c3FsaXRlX3V0aWxzL2hvb2tzcGVjcy5weQ==) | `100.00% <100.00%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/simonw/sqlite-utils/pull/573/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Simon+Willison)

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[simonw]

Glitch in the rendered documentation from https://sqlite-utils--573.org.readthedocs.build/en/573/plugins.html#prepare-connection-conn

[simonw]

https://sqlite-utils--573.org.readthedocs.build/en/573/plugins.html#prepare-connection-conn