feat: introduce a new node type - code block

sbroad-core/src/backend/sql/ir.rs

sbroad-core/src/backend/sql/tree.rs

sbroad-core/src/errors.rs

sbroad-core/src/executor.rs

sbroad-core/src/executor/ir.rs

sbroad-core/src/ir.rs

sbroad-core/src/ir/api/parameter.rs

sbroad-core/src/ir/block.rs

sbroad-core/src/ir/distribution.rs

sbroad-core/src/ir/expression/types.rs

sbroad-core/src/ir/tree/expression.rs

sbroad-core/src/ir/tree/relation.rs

sbroad-core/src/ir/tree/subtree.rs