Support out-of-tree runners

[pdgendt]

Is your enhancement proposal related to a problem? Please describe.

Zephyr modules can add custom West commands, but it is not possible to add ZephyrBinaryRunner subclass runners from modules.

Describe the solution you'd like

It should be possible to create a runner in a module, and be able to use it for out-of-tree boards.

Describe alternatives you've considered

None

Additional context

A PR like #81482 could benefit from this, as there is no in-tree board for the runner.
Similar for #80507 the runner could be added to the HAL

[henrikbrixandersen]

Duplicate of #23452?

[pdgendt]

Duplicate of #23452?

Yes, had to do a search first 🫣

The issue isn't entirely the same, will keep this for now.