fix: correctly map execute_many parameters for all drivers

[cofin]

Normalize mapping batches before parameter alignment so execute_many with list-of-dicts works with positional execution styles.

• The Problem: DuckDB (and other positional adapters) raised identifier/
  count mismatches when execute_many received a list of dicts for named
  placeholders.
• The Solution: Core parameter processor now converts mapping payloads
  to ordered positional values prior to validation; converter preserves
  unnamed placeholder ordinals; added regression tests.