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/readers/bun/README.md

@@ -64,6 +64,8 @@ The reader recognizes the following Bun struct tags:
 - `autoincrement` - Auto-increment column
 - `default` - Default value
 - `unique` - Unique constraint
+- `generated` - Generated column marker (`Generated`; expression is not in the tag)
+- `identity` - Identity column marker (`Identity`, `ALWAYS`)
 - `rel` - Relationship definition
 
 ## Example Bun Model