fix(types): restore return types and model returned sub-objects

Regenerated from the improved emitter:
- Methods that return a known object are typed as that object instead of
  `any` (verified against source) — sessions/checkouts/batches return their
  own class, stream factories return their stream class, etc.
- Objects the README documents under their own receiver (a server, socket,
  message, extension, or the autobase apply `host`) are now modeled as helper
  classes and wired to the method/callback that produces them, instead of
  being dropped.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: lucas-tortora

index.d.ts

@@ -170,12 +170,12 @@ export class Hyperdrive {
   /**
    * Get a read-only snapshot of a previous version.
    */
-  checkout(version: any): any
+  checkout(version: any): Hyperdrive
 
   /**
    * Useful for atomically mutate the drive, has the same interface as Hyperdrive.
    */
-  batch(): any
+  batch(): Hyperdrive
 
   setActive(bool: any): any