chore: simplify view comparison and remove pg_query_go

[tianzhou]

No description provided.

[Copilot]

Pull Request Overview

This PR simplifies view comparison logic by removing the AST-based semantic comparison in favor of direct string comparison. The change is based on the fact that both view definitions come from pg_get_viewdef() at the same PostgreSQL version, which provides normalized output, making complex AST comparison unnecessary.

Key Changes:

• Removed pg_query_go dependency and all AST-based comparison logic
• Simplified view comparison to use direct string matching
• Deleted comprehensive test suite for semantic view comparison

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
internal/diff/view_comparison_test.go	Removed entire test file containing semantic comparison tests
internal/diff/view.go	Removed pg_query_go import, simplified viewsEqual and generateModifyViewsSQL to use string comparison, deleted all AST comparison functions
go.mod	Removed pg_query_go/v6 and google.golang.org/protobuf dependencies

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