fix: return type of fountain generator

Author: LittleSound

packages/generate/src/base-generater.ts

@@ -17,7 +17,7 @@ export function createGeneraterWithRender<Result, RenderOptions>(createRender: C
       /**
        * Generate random encoded blocks that **never** ends
        */
-      *fountain(): Generator<Result> {
+      *fountain(): Generator<Result, never> {
         while (true) {
           _fountain ||= encoder.fountain()
           const block = _fountain.next().value

packages/luby-transform/src/encoder.ts

@@ -46,7 +46,7 @@ export class LtEncoder {
   /**
    * Generate random encoded blocks that **never** ends
    */
-  *fountain(): Generator<EncodedBlock> {
+  *fountain(): Generator<EncodedBlock, never> {
     while (true) {
       const degree = getRandomDegree(this.k)
       const selectedIndices = getRandomIndices(this.k, degree)