fix: httpx.Client is slow when sending large data

This commit addresses an issue where sending large data with httpx.Client was
extremely slow. The problem was that the entire data payload was being loaded
into memory and sent in a single operation.

This fix refactors the sending process for iterable bytes types to use a
chunked approach with `yield`, which significantly improves performance and
reduces memory usage for large payloads.

Signed-off-by: xiexianbin <me@xiexianbin.cn>

httpx/_content.py

@@ -61,7 +61,11 @@ class IteratorByteStream(SyncByteStream):
         else:
             # Otherwise iterate.
             for part in self._stream:
-                yield part
+                # For bytes types, should use yield to send data in
+                # chunks. Sending a very large part at once will
+                # result in extremely slow transmission.
+                for i in range(0, len(part), self.CHUNK_SIZE):
+                    yield part[i : i + self.CHUNK_SIZE]
 
 
 class AsyncIteratorByteStream(AsyncByteStream):