* Removed Python backend files that are no longer used (everything in `promptengine`)
* Added `providers` subdomain, with `CustomProviderProtocol`, `provider` decorator, and global singleton `ProviderRegistry`
* Added a tab for custom providers, and a dropzone, in ChainForge global settings UI
* List custom providers in the Global Settings screen once added.
* Added ability to remove custom providers by clicking X.
* Make custom funcs sync but call them async'ly.
* Add Cohere custom provider example in examples/
*Cache the custom provider scripts and load them upon page load
* Rebuild react and update package version
* Bug fix when custom provider is deleted and settings screen is opened on the deleted custom provider
