Support for lquery

[cemoktra]

Following the basic support for ltree, here is a PR to add a lquery struct (besides lquery would work with text too)

[cemoktra]

I did try to add tests like for the ltree but there is not comparison operator for lquery on postgres side

[abonander]

@cemoktra if you want to in a follow-up PR, you could add a regular #[sqlx::test] async fn to tests/postgres/types.rs which checks that PgLTree and PgLQuery function together in the database.