Enhance BulkChangeTable to support block wrappers

[thukim]

Previously, the BulkChangeTable RuboCop would fail to detect consecutive combinable operations if they were wrapped inside blocks like safety_assured, reversible, or other custom methods. This meant that we could miss opportunities to optimize our database migrations with bulk ALTER statements.
For example, the following code would not trigger an offense, even though the add_column calls could be combined:

def change
  safety_assured do
    add_column :users, :name, :string
    add_column :users, :email, :string
  end
end

This PR introduces a recursive AST traversal logic that efficiently navigates through nested block structures while preserving the operational context. The BulkChangeTable RuboCop now correctly identifies sequential combinable operations within a wide range of block patterns.

def change
  safety_assured do
    add_column :users, :name, :string
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ You can use `change_table :users, bulk: true` to combine alter queries.
    add_column :users, :email, :string
  end
end

Improvements:

• Rails Block Wrappers: Enhanced to support standard migration blocks, including: reversible (with dir.up and dir.down), up_only
• strong_migration support: Now correctly handles operations inside safety_assured blocks, a key feature of strong_migrations.
• Nested and Custom Blocks: The logic now correctly handles deeply nested blocks and custom wrapper methods (e.g., with_lock_retries). It is now more accurate in complex migrations, reducing the chances of missing bulkable operations.

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.