Prep for more model providers

Adds a `modelProvider` field to `promptVariants`, currently just set to "openai/ChatCompletion" for all variants for now.

Adds a `modelProviders/` directory where we can define and store pluggable model providers. Currently just OpenAI. Not everything is pluggable yet -- notably the code to actually generate completions hasn't been migrated to this setup yet.

Does a lot of work to get the types working. Prompts are now defined with a function `definePrompt(modelProvider, config)` instead of `prompt = config`. Added a script to migrate old prompt definitions.

This is still partial work, but the diff is large enough that I want to get it in. I don't think anything is broken but I haven't tested thoroughly.

src/components/RefinePromptModal/RefinePromptModal.tsx

@@ -25,6 +25,7 @@ import CompareFunctions from "./CompareFunctions";
 import { CustomInstructionsInput } from "./CustomInstructionsInput";
 import { type RefineOptionLabel, refineOptions } from "./refineOptions";
 import { RefineOption } from "./RefineOption";
+import { isObject, isString } from "lodash-es";
 
 export const RefinePromptModal = ({
   variant,
@@ -59,7 +60,12 @@ export const RefinePromptModal = ({
   const replaceVariantMutation = api.promptVariants.replaceVariant.useMutation();
 
   const [replaceVariant, replacementInProgress] = useHandledAsyncCallback(async () => {
-    if (!variant.experimentId || !refinedPromptFn) return;
+    if (
+      !variant.experimentId ||
+      !refinedPromptFn ||
+      (isObject(refinedPromptFn) && "status" in refinedPromptFn)
+    )
+      return;
     await replaceVariantMutation.mutateAsync({
       id: variant.id,
       constructFn: refinedPromptFn,
@@ -110,7 +116,7 @@ export const RefinePromptModal = ({
             </VStack>
             <CompareFunctions
               originalFunction={variant.constructFn}
-              newFunction={refinedPromptFn}
+              newFunction={isString(refinedPromptFn) ? refinedPromptFn : undefined}
             />
           </VStack>
         </ModalBody>