[improve][test] Add integration tests for the Canal source connector

## Current state

`canal` has **zero tests**.

## Proposal

Add a Testcontainers-based integration test: MySQL container (binlog enabled, as in `DebeziumMysqlSourceTest`) + a `canal/canal-server` container pointed at it, then assert the source emits change events for seeded rows.

_Part of an integration-test coverage sweep of all connector modules._

Start by reading DebeziumMysqlSourceTest and the Canal source connector module's existing test conventions. Set up the MySQL and canal/canal-server containers, seed rows, and verify that the source emits change events for them; the integration test should run reliably as part of the connector test suite.

Written by the indexing model from the issue text.