Cherrypick #35789 for 2.67.0: Fix timestamp issue in a yaml pipeline that calls SQL transform

[Amar3tto]

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Summary of Changes

Hello @Amar3tto, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request is a cherry-pick aimed at resolving a timestamp issue within YAML pipelines that utilize SQL transforms. My changes primarily focus on refining how schemas are handled, specifically ensuring that field types are accurately retrieved from cached schemas. Additionally, I've introduced a new test case to validate the correct behavior of CURRENT_TIMESTAMP when used in SQL transforms within these YAML-defined pipelines.

Highlights

• Schema Handling Improvement: Modified named_fields_to_schema in schemas.py to correctly retrieve field types from cached schemas, preventing potential type mismatches or re-inference issues when a schema has already been registered.
• YAML SQL Timestamp Test: Added a new test pipeline in sql.yaml to specifically validate the behavior of CURRENT_TIMESTAMP within a SQL transform when used in a YAML-defined pipeline, ensuring the fix addresses the reported timestamp issue.

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