[enhancement]: Default to Flashpack for v7

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Contact Details

_No response_

### What should this feature add?

[Flashpack](https://github.com/fal-ai/flashpack) is a high-throughput Diffusers-compatible weight storage format. It improves load times by between [3x and 20x](https://github.com/fal-ai/flashpack/blob/dc0e1fc8c6025dd0155a931f16e31829513ec2c0/README.md#production-numbers) versus Safetensors. It currently supports quantized Diffusers models and may add a single-file offline distribution option in the future (https://github.com/fal-ai/flashpack/pull/32).

You may wish to consider defaulting to Flashpack in version 7 and providing Flashpack versions of the various Starter Models, with SDNQ for quantization as required. This would potentially improve Invoke's time-to-first-generation speed considerably, particularly on lower-end systems where such enhancements are most important.

### Alternatives

_No response_

### Additional Content

_No response_