fix: properly load dbt relation type for get_relation() and related functions

[newtonapple]

fixes #1987

[Copilot]

Pull Request Overview

This PR fixes the proper loading of dbt relation types for get_relation() and related functions by ensuring that relation type information (table vs view) is correctly populated when retrieving data objects.

• Refactored _data_object_to_relation() method to centralize relation creation logic
• Updated load_relation() to use data object information when available for proper type detection
• Enhanced test coverage to verify relation type detection for both tables and views

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
sqlmesh/dbt/adapter.py	Refactored relation creation logic and updated load_relation() to properly detect relation types
tests/dbt/test_adapter.py	Added test coverage for relation type detection and updated existing test expectations

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