feat(dsql): parse ALTER COLUMN SET STORAGE

[amaksimo]

Summary

• add a typed AlterColumnOperation::SetStorage AST variant
• parse and format PostgreSQL storage modes PLAIN, EXTERNAL, EXTENDED, MAIN, and DEFAULT
• support both ALTER COLUMN name and PostgreSQL shorthand ALTER name
• bump sqlparser-dsql to 0.62.3 for release

Validation

• cargo fmt --all -- --check
• cargo test
• cargo test --all-features
• cargo clippy --all-targets --all-features -- -D warnings
• cargo package --allow-dirty