GeezerVison

Updates #2997.

sqlc.embed(t) on the nullable side of an outer join generates code that compiles but fails at runtime when the row is missing (converting NULL to string is unsupported). The embedded struct is the table's model, so its fields aren't nullable.

Plain columns are already made nullable by isTableRequired, but embeds skipped it because their column has no Table. generate now fails for this case instead:

query.sql:2:23: sqlc.embed(u) on the nullable side of an outer join is not supported

The join rules are the same as for plain columns (LEFT, RIGHT, FULL). Embed.Param() is new so a self join like users a LEFT JOIN users b can be told apart by alias.

This only turns the runtime failure into a generate-time error, as #2858 did. A real fix needs a design choice (#2348). It is a breaking change for queries that work today because they never hit a missing row.

Limits:

• Only the top-level FROM is checked, like plain columns, so embeds inside subqueries or CTEs are not covered.
• It only applies to the default analyzer. With a database analyzer (database: in the config) inference errors are discarded by design, so the query still generates as before. The error cases run in the base context only for that reason.
• The analysis core (SQLC_TEST_CORE) doesn't support embeds yet.

Test

New end-to-end cases internal/endtoend/testdata/sqlc_embed_outer_join_*: left (SQLite, PostgreSQL), right and self expect the error, ok still generates. The four error cases fail without the change.