fix: include schema temp table

[eakmanrq]

BQ requires a schema defined when creating the temp table and we want to ensure it gets created in the same place as the target physical schema.

https://tobiko-data.slack.com/archives/C044BRE5W4S/p1760530731990029

[Copilot]

Pull Request Overview

This PR fixes a BigQuery requirement where temporary tables need to be created with an explicit schema defined, ensuring they are created in the same location as the target physical schema.

• Updates temporary table creation in _get_target_and_source_columns to include the model's physical schema
• Adds comprehensive test coverage to verify the temp table creation includes the correct schema

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
sqlmesh/core/snapshot/evaluator.py	Modified temp table creation to include physical schema for BQ compatibility
tests/core/test_snapshot_evaluator.py	Added test to verify temp table creation with schema when using IGNORE change policies

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