Improve support for remote loading and saving.

[copybara-service]

Improve support for remote loading and saving.

• _support_gcs_uri did not work for saving APIs. It would create a temp folder, but the file created in the temp folder would never actually be copied to the remote path. Introduced a SupportWriteToRemote, a context manager that copies the temp file to remote on exit and cleans up the temp folder.
• there were several different places handling remote loading, but none of them would clean up the temp folders created. Introduced a SupportWriteToRemote, a context manager that copies the remote file to a temp folder and cleans up on exit.
• removed ad-hoc support for remote zip file saving, instead, this is handled the same way as other remote saving cases with a temp file, which removes the memory requirement.