chore: check schema when create table branch

[zhyass]

I hereby agree to the terms of the CLA available at: https://docs.databend.com/dev/policies/cla/

Summary

This PR tightens schema safety guarantees around table branches by introducing additional validation in branch creation and schema-altering operations.

1. Branch creation schema validation

When creating a branch, the system now verifies that the snapshot used as the branch base has the same schema as the current table.
If the schemas differ, branch creation will fail with an explicit error.
This prevents branches from being created on top of incompatible or outdated schemas.

2. Restrict schema rebuild operations with active branches

For ADD COLUMN and MODIFY COLUMN operations that require data rebuild, the system now checks whether the table has any active branches.
If active branches exist, the operation is rejected.
This avoids introducing inconsistencies between the main table and its branches during schema-altering rebuilds.

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe): enhance

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This change is 

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[zhyass]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Chef's kiss.

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