feat: add HookData for baml react hooks (#1925)

This adds a new helper type called `HookData` to be able to quickly
perform NonNullable type passing like this example:

```tsx

function Component({ data }: HookData<'TestOpenAi'>) {
  // data is the NonNull return type of HookOutput<'TestOpenAi'>['data']
}
```
<!-- ELLIPSIS_HIDDEN -->


----

> [!IMPORTANT]
> Add `HookData` type for non-nullable data handling in BAML React hooks
and update documentation.
> 
>   - **TypeScript**:
> - Add `HookData` type in `hooks.tsx.j2` and `hooks.tsx` for
non-nullable data handling in BAML React hooks.
>   - **Documentation**:
>     - Add `hook-data.mdx` for `HookData` type reference and examples.
> - Update `docs.yml` to include `HookData` documentation in navigation.
> 
> <sup>This description was created by </sup>[<img alt="Ellipsis"
src="https://img.shields.io/badge/Ellipsis-blue?color=175173">](https://www.ellipsis.dev?ref=BoundaryML%2Fbaml&utm_source=github&utm_medium=referral)<sup>
for e37ea4d. You can
[customize](https://app.ellipsis.dev/BoundaryML/settings/summaries) this
summary. It will automatically update as commits are pushed.</sup>


<!-- ELLIPSIS_HIDDEN -->

Author: seawatts

engine/language_client_codegen/src/typescript/templates/react/hooks.tsx.j2

@@ -81,6 +81,8 @@ export type HookOutput<FunctionName extends FunctionNames = FunctionNames, Optio
   reset: () => void
 }
 
+export type HookData<FunctionName extends FunctionNames, Options extends { stream?: boolean } = { stream?: true }> = NonNullable<HookOutput<FunctionName, Options>['data']>;
+
 /**
  * Type guard to check if the hook props are configured for streaming mode.
  *

fern/03-reference/baml_client/react-nextjs/hook-data.mdx

@@ -24,17 +24,17 @@ ai-chat:
       // Optional string fields use ?
       // @description is optional, but if you include it, it goes after the field.
       name string? @description("The name of the object")
-      
+
       // Arrays of primitives
       // arrays cannot be optional.
       tags string[]
-      
+
       // Enums must be declared separately and are optional
       status MyEnum?
-      
+
       // Union types
       type "success" | "error"
-      
+
       // Primitive types
       count int
       enabled bool
@@ -67,7 +67,7 @@ ai-chat:
       // prompt with jinja syntax inside here. with double curly braces for variables.
       // make sure to include: {{ ctx.output_format }} in the prompt, which prints the output schema instructions so the LLM returns the output in the correct format (json or string, etc.). DO NOT write the output schema manually.
       prompt #"
-        
+
       "#
     }
 
@@ -83,7 +83,7 @@ ai-chat:
 
     <Prompt>
       In case you need to write a prompt example:
-      1. Make sure to include the input in the prompt (even if it's an image) using {{ input }}  
+      1. Make sure to include the input in the prompt (even if it's an image) using {{ input }}
       2. Make sure to include {{ ctx.output_format }} in the prompt so the LLM knows how to format the output.
       3. You do not need to specify to "answer in JSON format". Only write in the prompt brief instruction, and any other task-specific things to keep in mind for the task.
       4. Write a {{ _.role("user") }} tag to indicate where the user's inputs start. So if there's a convo you can write
@@ -162,10 +162,10 @@ ai-chat:
     }
 
     class WeatherAPI {
-      city string @description("the user's city") 
+      city string @description("the user's city")
       timeOfDay string @description("As an ISO8601 timestamp")
     }
-    
+
     // Function that can return different tool classes
     function UseTool(user_messages: ChatMessage[]) -> WeatherAPI | MyOtherAPI {
       client CustomSonnet
@@ -190,7 +190,7 @@ ai-chat:
     async def main():
         tool = b.UseTool("What's the weather like in San Francisco?")
         print(tool)
-        
+
         if isinstance(tool, WeatherAPI):
             print(f"Weather API called:")
             print(f"City: {tool.city}")
@@ -219,7 +219,7 @@ ai-chat:
     print(collector.last.usage)  # Print usage metrics
     print(collector.last.raw_llm_response)  # Print final response as string
     # since there may be retries, print the last http response received
-    print(collector.last.calls[-1].http_response) 
+    print(collector.last.calls[-1].http_response)
     ```
 
     ```typescript
@@ -696,6 +696,8 @@ navigation:
                 path: 03-reference/baml_client/react-nextjs/hook-input.mdx
               - page: HookOutput
                 path: 03-reference/baml_client/react-nextjs/hook-output.mdx
+              - page: HookData
+                path: 03-reference/baml_client/react-nextjs/hook-data.mdx
       - section: Attributes
         contents:
           - page: What are attributes?