Implement notransaction option and wrap statement errors

[ftkg]

This addresses some niggles we face in Satori migrations (eg. running CREATE INDEX CONCURRENTLY).

The PlannedMigration.DisableTransaction flag was already parsed and available, this PR branches on it by running their statements directly through the connection.

Also, statement/begin errors returned a bare error with no migration context. This wraps every failure in the existing TxError, carrying the migration id.

[Copilot]

Pull request overview

Adds support for notransaction migrations by executing planned statements directly on the connection (skipping BEGIN/COMMIT), and improves error reporting by consistently attaching migration context via TxError.

Changes:

• Execute migrations without a surrounding transaction when PlannedMigration.DisableTransaction is set.
• Wrap statement execution and transaction-begin failures in TxError for better migration-id context.
• Add parser/tests/docs coverage for notransaction behavior and its non-atomic implications.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
sqlparse/sqlparse_test.go	Adds tests ensuring notransaction is parsed correctly for Up vs Down sections.
README.md	Documents notransaction semantics, limitations, and interaction with statement blocks.
migrate.go	Implements non-transactional execution path and centralizes execution/recording in runMigration.
migrate_test.go	Adds integration tests verifying non-transactional behavior (no rollback) and tracking-table recording.

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