Keep discovery running for mixed topic selectors

[Old-Ding]

Summary

• preserve the early-stop optimization only when explicit topics are the sole inclusive selector
• keep discovery active when topics are combined with regex, type, service, action, all, or static-topic selectors
• add a regression test where a regex topic is subscribed before a later explicit topic appears

Fixes #2417

Testing

• git diff --check
• not run locally: test_record_regex requires a ROS 2/colcon environment that is not available on this machine