feat: generated and identity columns for mssql, sqlite, drizzle, typeorm, bun and gorm readers

- mssql: write computed columns (AS (expr) PERSISTED) and identity; read computed definition and identity
- sqlite: write GENERATED ALWAYS AS (expr) STORED; read generated columns via table_xinfo and parse the expression
- drizzle: generatedAlwaysAs / generated(Always|ByDefault)AsIdentity, read and write
- typeorm: asExpression/generatedType and identity decorators, read and write; decorator scan is now quote-aware
- bun, gorm readers: read generated and identity markers
- readmes updated

pkg/writers/sqlite/README.md

@@ -229,6 +229,7 @@ func main() {
 
 ## Notes
 
+- Generated columns are written as `col TYPE GENERATED ALWAYS AS (expr) STORED` (no DEFAULT)
 - Schema flattening is **always enabled** for SQLite output (cannot be disabled); the default schema (`public`/`main`) produces bare table names, other schemas are prefixed
 - Constraint and index names are prefixed with the flattened table name to avoid collisions
 - Generated SQL is compatible with SQLite 3.x