fix(c/driver/postgresql): bind null parameters

[Mandukhai-Alimaa]

• Infer PostgreSQL parameter types via PREPARE (no OIDs) + DESCRIBE, then reconcile with Arrow bind schema.
• Bind Arrow NA (all-null) parameters as PostgreSQL’s expected parameter type.
• Don’t force a type when PostgreSQL can’t infer/returns unknown. Fall back without error.
• Add writer support for Arrow NA and add tests for null parameter binding.

Closes #3549