Fix remote worker job processing

[bstrdsmkr]

When using remote workers, the GuzzleHttp client isn't found in the namespace, add a \ to use the global namespace

Files waiting on remote workers are copied into the inprogress directory, but the remote api looks for them in the inbox directory

[williamjallen]

These changes seem reasonable to me, although it looks like you need to remove some errors from the PHPStan baseline. You can do that with vendor/bin/phpstan analyse --memory-limit=8G --generate-baseline. @zackgalbreath is more familiar with this feature than I am, and should do a final review before this can be merged.

[zackgalbreath]

I confirmed locally that this functionality was broken, and that this PR fixes it.

Thanks for the contribution, @bstrdsmkr !