feat: bind null query parameters and verify generation on PostgreSQL

[omer-cengel]

Summary

Generated query methods can now pass null arguments to the runtime, and the
whole compiler pipeline is exercised against a real PostgreSQL instance instead
of an in-memory database only. Previously a generated method rejected a null
argument while assembling its parameter list, so a nullable column could never
be written as null through generated code.

Changes

• Generated methods collect executor arguments in a null-tolerant fixed-size
  list, so a null argument reaches the JDBC runtime and is bound as SQL NULL.
• Added an end-to-end integration test that runs the accepted schema snapshot as
  real PostgreSQL DDL, compiles the generated Java, and executes the generated
  classes through the JDBC runtime for typed reads and writes.
• The integration test writes an all-NULL row through a generated write method
  and reads it back through a generated read method, covering SMALLINT,
  VARCHAR, TEXT, BOOLEAN, DATE, TIMESTAMP, and DECIMAL.
• Added test-scoped PostgreSQL driver and container dependencies, and pinned a
  transitive compression dependency to a version without known advisories.
• The PostgreSQL tests are skipped, not failed, when no container runtime is
  available, so the suite still runs on machines without one.

Scope and non-goals

• Generated class names, method signatures, parameter names, result records,
  imports, and the executor and row-mapper runtime interfaces are unchanged.
• No new SQL types, schema forms, or query shapes are accepted; the tests
  exercise the already-supported subset.
• RETURNING, transactions, and additional PostgreSQL types remain unsupported.