Test migration rollback instructions

[Aaron1011]

I've added two different tests:

• Run 'apply; rollback; apply' for each migration in sequence, and check that everything succeeds
• Run a "painter's algorithm"-type test, where we apply all migrations up to N (inclusive), and check that we can rollback N

In order to run the rollback instructions programatically, I modified them to use '/* */'-style comments on the same line as the actual commands, since ClickHouse rejects sending a comment as a standalone query.

The only non-trivial change to rollback instructions is in Migation0008

• we cannot rollback the change to 'BatchRequest.errors', since we cannot convert an Array back to a Map. There should be no data in this table when this particular migration runs, so this is fine

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[!IMPORTANT] Add tests for migration rollback instructions and modify rollback comments for compatibility in ClickHouse migration manager.

• Tests:
  • Add tests for migration rollback instructions in clickhouse.rs.
  • Test apply; rollback; apply sequence for each migration.
  • Test rollback for all migrations up to N and ensure rollback of N.
• Rollback Instructions:
  • Modify rollback instructions to use inline /* */ comments in migration_trait.rs and various migration files.
  • Cannot rollback BatchRequest.errors in Migration0008 due to data type limitations.
• Misc:
  • Add NUM_MIGRATIONS constant in mod.rs to ensure test consistency.
  • Update make_all_migrations to assert migration count matches NUM_MIGRATIONS.

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