Support embed type annotation

[LouisGariepy]

Migrated from halcyonnouveau/clorinde#139, originally reported by @Folyd on 2025-06-20.

For example:

--: Author(age?)

--! authors : Author
SELECT name, age FROM Authors;

--! authors_from_country (country?) : (age?)
SELECT a.*, COUNT(*) OVER() as total_count
FROM Authors as a
WHERE a.nationality = :country;

--! authors_from_country (country?) : Author
SELECT a.*, COUNT(*) OVER() as total_count
FROM Authors as a
WHERE a.nationality = :country;

The authors_from_country return all author columns plus an extra total_account, currently we need to declare (age?) as the type annotation. I hope to support embed another type into here, such as Author

Even further:

--: Author(age?)
--: Country(gdp?)
--! authors_from_country (country?) : Author + Country
SELECT a.*, 
c.*,
COUNT(*) OVER() as total_count
FROM Authors as a
FROM Country as c JOIN a.nationality = c.id
WHERE a.nationality = :country;