%%bash: read from stream until separator found or buffer is full (#14019)

Original issue: https://github.com/ipython/ipython/issues/14005
TLDR before we would read line by line however this is not necessary and
we should just continue reading until we reach EOF.

The case we patch here is if we read a line larger than the allowed
buffer size, we will return that chunk (aka the entire buffer) to be
written out and still continue reading.

IPython/core/magics/script.py

@@ -4,6 +4,7 b''
 # Distributed under the terms of the Modified BSD License.
 
 import asyncio
+import asyncio.exceptions
 import atexit
 import errno
 import os
@@ -208,15 +209,23 b' class ScriptMagics(Magics):'
             """Call a coroutine on the asyncio thread"""
             return asyncio.run_coroutine_threadsafe(coro, event_loop).result()
 
+        async def _readchunk(stream):
+            try:
+                return await stream.readuntil(b"\n")
+            except asyncio.exceptions.IncompleteReadError as e:
+                return e.partial
+            except asyncio.exceptions.LimitOverrunError as e:
+                return await stream.read(e.consumed)
+
         async def _handle_stream(stream, stream_arg, file_object):
             while True:
-                line = (await stream.readline()).decode("utf8", errors="replace")
-                if not line:
+                chunk = (await _readchunk(stream)).decode("utf8", errors="replace")
+                if not chunk:
                     break
                 if stream_arg:
-                    self.shell.user_ns[stream_arg] = line
+                    self.shell.user_ns[stream_arg] = chunk
                 else:
-                    file_object.write(line)
+                    file_object.write(chunk)
                     file_object.flush()
 
         async def _stream_communicate(process, cell):