Remove unnecessary indirection

Also updated some psalm params and returns.

lib/AsyncGenerator.php

@@ -6,6 +6,9 @@ namespace Amp;
  * @template TValue
  * @template TSend
  * @template TReturn
+ *
+ * @template-implements Pipeline<TValue>
+ * @template-implements \IteratorAggregate<int, TValue>
  */
 final class AsyncGenerator implements Pipeline, \IteratorAggregate
 {
@@ -73,6 +76,8 @@ final class AsyncGenerator implements Pipeline, \IteratorAggregate
 
     /**
      * @inheritDoc
+     *
+     * @psalm-return TValue|null
      */
     public function continue(): mixed
     {
@@ -135,10 +140,12 @@ final class AsyncGenerator implements Pipeline, \IteratorAggregate
 
     /**
      * @inheritDoc
+     *
+     * @paslm-return \Iterator<int, TValue>
      */
     public function getIterator(): \Iterator
     {
-        while (null !== $value = $this->continue()) {
+        while (null !== $value = $this->source->continue()) {
             yield $value;
         }
     }

lib/Internal/AutoDisposingPipeline.php

@@ -12,6 +12,7 @@ use Amp\Pipeline;
  *
  * @template-covariant TValue
  * @template-implements Pipeline<TValue>
+ * @template-implements \IteratorAggregate<int, TValue>
  */
 final class AutoDisposingPipeline implements Pipeline, \IteratorAggregate
 {
@@ -46,10 +47,12 @@ final class AutoDisposingPipeline implements Pipeline, \IteratorAggregate
 
     /**
      * @inheritDoc
+     *
+     * @psalm-return \Iterator<int, TValue>
      */
     public function getIterator(): \Iterator
     {
-        while (null !== $value = $this->continue()) {
+        while (null !== $value = $this->source->continue()) {
             yield $value;
         }
     }

lib/Pipeline.php

@@ -17,7 +17,7 @@ interface Pipeline extends \Traversable
      *
      * @return mixed Returns null if the pipeline has completed.
      *
-     * @psalm-return TValue
+     * @psalm-return TValue|null
      *
      * @throws \Throwable The exception used to fail the pipeline.
      */

lib/PipelineSource.php

@@ -56,6 +56,8 @@ final class PipelineSource
      *
      * @param mixed $value
      *
+     * @psalm-param TValue $value
+     *
      * @throws DisposedException Thrown if the pipeline is disposed.
      */
     public function yield(mixed $value): void