[Feature] Integration tests - SSH shell PM

[miruuna]

Description

This is a sub-issue of #726.

An integration testing framework to ensure that drunc executes correctly in an SSH shell environment, with default options, and produces the expected output/state transitions. Currently, the integration tests validate the basic commands (boot-> conf -> start etc.) without any options. The new integration tests in ./integtest/ should test the command sequence with the following parameters:

• command targeting and subsequent behaviour
• including and excluding
• flushing processes and subsequent behaviour
• command sequences
• manual error introductions
  etc.

Potential impact radius

Small/Isolated

Reason for change

Validate that drunc workflow works reliably on different platforms and ensure new changes don't break functionality.

Suggested implementations

• new ./integtest directory to contain integration tests
• use CLIRunner to run each command via SSH shell PM
• use --integtest-ssh-shell marker to run the tests
• check outputs and state transitions
• capture CLI outout using tee for validation

Testing suggestions

No response

Anything else?

No response