more stable fp16 training

use native url_to_fs provided by fsspec

default saving and loading to local file system, current folder

support checkpointing to s3

make checkpoints able to save to google storage by passing in gs://<b…

…ucket>/<folder> to checkpoint_path in trainer

make checkpoints able to save to google storage by passing in gs://<b…

…ucket>/<folder> to checkpoint_path in trainer

make checkpoints able to save to google storage by passing in gs://<b…

…ucket>/<folder> to checkpoint_path in trainer

some more cleanup, in prep for gcsfs

complete local / cloud filesystem agnostic saving and loading of chec…

…kpoints, thanks to @rom1504

add the component from unet squared paper that seems to be doing some…

…thing visible