xyz_grid: support refiner_checkpoint and refiner_switch_at

Update SD XL commit hash

Fix typo in shared_options.py

separate Extra options

unperdictable -> unpredictable

Add RES sampler and reorder the sampler list

Fix MHA error with ex_bias and support ex_bias for layers which don't have bias

Fixes for `git checkout`, MPS/macOS fixes and optimizations

Fix typo in launch_utils.py

existance -> existence

add new callback for scripts to be used before processing

For MPS, using a tensor created with `torch.empty()` can cause `torch.baddbmm()` to include NaNs in the tensor it returns, even though `beta=0`. However, with a tensor of shape [1,1,1], there should be a negligible performance difference between `torch.empty()` and `torch.zeros()` anyway, so it's better to just use `torch.zeros()` for this and avoid unnecessarily creating issues.

Even if this causes chunks to be much smaller, performance isn't significantly impacted. This will usually reduce memory usage but should also help with poor performance when free memory is low.