Patch Release v0.21.1: Fix import and config loading for `from_single_file`

• Fix model offload bug when key isn't present by @DN6 in #5030
• [Import] Don't force transformers to be installed by @patrickvonplaten in #5035
• allow loading of sd models from safetensors without online lookups using local config files by @vladmandic in #5019
• [Import] Add missing settings / Correct some dummy imports by @patrickvonplaten in #5036