Add RADIO backbones

[liopeer]

What has changed and why?

• adds support for RADIO backbones
• documents them
• it's not super clean yet, but it's usable for distillation/linear segmentation. in a follow-up I would add the ability to get intermediate features so that it can be used with LT-DETR and I would do some clean-up

How has it been tested?

• unit tests and notebook

Did you update CHANGELOG.md?

• Yes
• Not needed (internal change)

Did you update the documentation?

• Yes
• Not needed (internal change without effects for user)

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[liopeer]

/review