[multiprocessing] Add support of PipeConnection to the Listener and top-level connection functions

[sergey-miryanov]

For the AF_PIPE address family, Listener._listener will be a PipeListener, and its accept() method returns a PipeConnection.

PipeConnection shares a base class with Connection but is a distinct class. As a result, the current type annotations don't work correctly:

• Listener.accept should return Connection | PipeConnection
• deliver_challenge, answer_challenge, and wait should accept Connection | PipeConnection

The same applies to Client as well:

• Client should return Connection | PipeConnection

Tested on Windows 11, Python 3.15.0b1

[srittau]

PR welcome, although we should probably just accept _ConnectionBase in argument positions. And since PipeConnection only exists on win32 we need conditional branches for the functions that return connections.

[alexeev-prog]

Can you assign me?

[sergey-miryanov]

Thanks all!