Function alter_sql 

pub fn alter_sql(table: &str, diff: &SchemaDiff, force: bool) -> String

Render an ALTER TABLE migration that reconciles table to its declared shape.

Added columns are emitted nullable (not NOT NULL) even though Gize’s create tables are NOT NULL: adding a NOT NULL column without a default to a table that may hold rows fails, so the safe move is a nullable column plus a -- TODO to backfill and tighten (ADR-011 revision). Drops are only included when force is set.