With the long due#102896, we can finally add tests forinteract command.

However, the currentinteract command usescode.interact directly which makes it super difficult to test, becausecode.interact writes tosys.stderr directly (withsys.stderr.write)! We need to overload thewrite method in a derived class to write to the same channel asPdb.message.

The interactive message is also changed to make more sense - one might wonder if this is a breaking change to users, but

1. This PR will be not backported, so it's a new thing.
2. The current status (plus the interactive issue ingh-102895 Add an option local_exit in code.interact to block exit() from terminating the whole process #102896 before the fix) made it almost impossible to write tests forinteract command, so I don't think we'll break anything.

This PR adds the class for interact commmand and some basic tests forinteract; and also clarifies the namespace situation withinteract - it's a bit tricky and could be confusing to the users, so some clarification is needed.

The way to exitinteract command is also added to the docs.

• Issue:Improve test coverage on pdb #102980

📚 Documentation preview 📚:https://cpython-previews--111194.org.readthedocs.build/