feat(nodes): add freeu support

Add support for FreeU. See:
- https://huggingface.co/docs/diffusers/main/en/using-diffusers/freeu
- https://github.com/ChenyangSi/FreeU

Implementation:
- `ModelPatcher.apply_freeu()` handles the enabling freeu (which is very simple with diffusers).
- `FreeUConfig` model added to hold the hyperparameters.
- `freeu_config` added as optional sub-field on `UNetField`.
- `FreeUInvocation` added, works like LoRA - chain it to add the FreeU config to the UNet
- No support for model-dependent presets, this will be a future workflow editor enhancement

Closes #4845

invokeai/app/invocations/latent.py

@@ -655,6 +655,7 @@ class DenoiseLatentsInvocation(BaseInvocation):
             with (
                 ExitStack() as exit_stack,
                 ModelPatcher.apply_lora_unet(unet_info.context.model, _lora_loader()),
+                ModelPatcher.apply_freeu(unet_info.context.model, self.unet.freeu_config),
                 set_seamless(unet_info.context.model, self.unet.seamless_axes),
                 unet_info as unet,
             ):