Remove a few unnecessary casts from Stream (#55147)

src/libraries/System.Private.CoreLib/src/System/IO/Stream.cs

@@ -201,7 +201,7 @@ public virtual ValueTask DisposeAsync()
         public virtual IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback? callback, object? state) =>
             BeginReadInternal(buffer, offset, count, callback, state, serializeAsynchronously: false, apm: true);
 
-        internal IAsyncResult BeginReadInternal(
+        internal Task<int> BeginReadInternal(
             byte[] buffer, int offset, int count, AsyncCallback? callback, object? state,
             bool serializeAsynchronously, bool apm)
         {
@@ -231,7 +231,7 @@ public virtual ValueTask DisposeAsync()
 
             // Create the task to asynchronously do a Read.  This task serves both
             // as the asynchronous work item and as the IAsyncResult returned to the user.
-            var asyncResult = new ReadWriteTask(true /*isRead*/, apm, delegate
+            var task = new ReadWriteTask(true /*isRead*/, apm, delegate
             {
                 // The ReadWriteTask stores all of the parameters to pass to Read.
                 // As we're currently inside of it, we can get the current task
@@ -262,14 +262,14 @@ public virtual ValueTask DisposeAsync()
             // Schedule it
             if (semaphoreTask != null)
             {
-                RunReadWriteTaskWhenReady(semaphoreTask, asyncResult);
+                RunReadWriteTaskWhenReady(semaphoreTask, task);
             }
             else
             {
-                RunReadWriteTask(asyncResult);
+                RunReadWriteTask(task);
             }
 
-            return asyncResult; // return it
+            return task; // return it
         }
 
         public virtual int EndRead(IAsyncResult asyncResult)
@@ -338,7 +338,7 @@ private Task<int> BeginEndReadAsync(byte[] buffer, int offset, int count)
             {
                 // If the Stream does not override Begin/EndRead, then we can take an optimized path
                 // that skips an extra layer of tasks / IAsyncResults.
-                return (Task<int>)BeginReadInternal(buffer, offset, count, null, null, serializeAsynchronously: true, apm: false);
+                return BeginReadInternal(buffer, offset, count, null, null, serializeAsynchronously: true, apm: false);
             }
 
             // Otherwise, we need to wrap calls to Begin/EndWrite to ensure we use the derived type's functionality.
@@ -358,7 +358,7 @@ private struct ReadWriteParameters // struct for arguments to Read and Write cal
         public virtual IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback? callback, object? state) =>
             BeginWriteInternal(buffer, offset, count, callback, state, serializeAsynchronously: false, apm: true);
 
-        internal IAsyncResult BeginWriteInternal(
+        internal Task BeginWriteInternal(
             byte[] buffer, int offset, int count, AsyncCallback? callback, object? state,
             bool serializeAsynchronously, bool apm)
         {
@@ -388,7 +388,7 @@ private struct ReadWriteParameters // struct for arguments to Read and Write cal
 
             // Create the task to asynchronously do a Write.  This task serves both
             // as the asynchronous work item and as the IAsyncResult returned to the user.
-            var asyncResult = new ReadWriteTask(false /*isRead*/, apm, delegate
+            var task = new ReadWriteTask(false /*isRead*/, apm, delegate
             {
                 // The ReadWriteTask stores all of the parameters to pass to Write.
                 // As we're currently inside of it, we can get the current task
@@ -420,14 +420,14 @@ private struct ReadWriteParameters // struct for arguments to Read and Write cal
             // Schedule it
             if (semaphoreTask != null)
             {
-                RunReadWriteTaskWhenReady(semaphoreTask, asyncResult);
+                RunReadWriteTaskWhenReady(semaphoreTask, task);
             }
             else
             {
-                RunReadWriteTask(asyncResult);
+                RunReadWriteTask(task);
             }
 
-            return asyncResult; // return it
+            return task; // return it
         }
 
         private static void RunReadWriteTaskWhenReady(Task asyncWaiter, ReadWriteTask readWriteTask)
@@ -642,7 +642,7 @@ private Task BeginEndWriteAsync(byte[] buffer, int offset, int count)
             {
                 // If the Stream does not override Begin/EndWrite, then we can take an optimized path
                 // that skips an extra layer of tasks / IAsyncResults.
-                return (Task)BeginWriteInternal(buffer, offset, count, null, null, serializeAsynchronously: true, apm: false);
+                return BeginWriteInternal(buffer, offset, count, null, null, serializeAsynchronously: true, apm: false);
             }
 
             // Otherwise, we need to wrap calls to Begin/EndWrite to ensure we use the derived type's functionality.