refactor(generator): use poet statement types instead of RawStmt

Replace RawStmt usage with structured statement types where applicable:
- poet.Return for return statements
- poet.Switch for switch statements
- poet.If for if statements

Also:
- Use Pointer field on Param instead of "*" prefix in Type
- Format multi-value switch cases on separate lines
- Keep line lengths under 90 chars for readability

This makes the code generation more structured and type-safe while
maintaining identical output.

Author: claude