Feature Description
Predicate pushdown has now been implemented and tested in stackql/any-sdk.
We need to replicate those predicate-pushdown tests — along with their corresponding registry provider configurations — into the main branch of the stackql repo as additional robot tests.

This issue covers:

• Reviewing the predicate pushdown tests in any-sdk:
  https://github.com/stackql/any-sdk
• Mirroring equivalent test scenarios in the stackql robot test suite
• Ensuring provider registry definitions used in any-sdk tests are ported or adapted as needed for the stackql environment
• Validating that pushdown optimizations behave the same way in the full StackQL execution engine

@claude Please review the predicate-pushdown implementation and test suite in any-sdk, identify the exact tests and provider configurations that need to be replicated in the stackql project, and propose a structured plan and implement them as robot tests within the stackql repository (main branch).