Add integration tests for SQLite json -> and ->> operators

[zaveshaa]

Issue #4366 asked for integration coverage of the SQLite json -> and ->> operators. The operators exist but only doc-tests cover them.

These integration tests add:

• -> (retrieve_as_object_sqlite) with a JSON path and an integer index, on Json and Jsonb
• ->> (retrieve_as_text) with a JSON path and an array index, plus the NULL case for a missing path

Relates to #4366.

[weiznich]

Thanks for opening this PR. Could you explain the motivation to add these tests? For me it looks like that this behaviour is already tested by the doc-tests, so the tests look rather duplicated to me?

[zaveshaa]

Good point. The doc-tests cover the basic behaviour of -> and ->> on Json, but they run in-memory and don't hit a real database with the JSON path/index variants. Issue #4366 asked for integration coverage since the doc-tests only exercise the simplest case.

That said, if you think the doc-tests already cover this well enough, I'm fine dropping the PR — no point adding redundant tests. Let me know which way you'd rather go.