Avoid duplicate PyREPL hook registration and clarify hook names

[edvilme]

Problem

The PyREPL exception and display hooks in python_files/pythonrc.py are registered twice. Their current my_excepthook and my_displayhook names also do not communicate that they provide VS Code integration, which makes the registration flow harder to understand and maintain.

Expected behavior

The hooks should have a single registration path, and their names should clearly describe their VS Code-specific purpose.

Acceptance criteria

• Register the PyREPL exception and display hooks exactly once.
• Rename the hooks to clearly identify their VS Code integration role.
• Update the related shell integration tests to use and verify the descriptive names.

Related pull request

• Pythonrc: Don't register PyREPL hooks twice #26145