Spandrel: "prefer half" instead of "force half"

[akx]

Description

As discussed with the Spandrel folks, it's good to heed Spandrel's "supports half precision" flag to avoid e.g. black blotches and what-not.

This is why spandrel has the supports_half tag. Transformer models typically don't work well with fp16

• which issues it fixes, if any
  • None yet, since the current experimental HAT code doesn't set half=True, but if it did, HAT would have a bad time

Screenshots/videos:

None.

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests