Add data producer helpers for linear and exponential data

[tkilias]

Goal

Provide high-level helpers that execute generated benchmark-data SQL.

Scope

• Execute the existing linear and exponential SQL statements through QueryFunc.
• Preserve the current SQL-generator APIs and behavior.

Acceptance Criteria

• Helpers execute statements in generated order.
• Existing generator behavior and validation remain backward-compatible.
• Unit tests cover execution order and invalid inputs.