gh-129005: Remove copies from _pyio using take_bytes (#141539)

Memory usage now matches that of _io for large files.

Lib/_pyio.py

@@ -546,7 +546,7 @@ def nreadahead():
             res += b
             if res.endswith(b"\n"):
                 break
-        return bytes(res)
+        return res.take_bytes()
 
     def __iter__(self):
         self._checkClosed()
@@ -620,7 +620,7 @@ def read(self, size=-1):
         if n < 0 or n > len(b):
             raise ValueError(f"readinto returned {n} outside buffer size {len(b)}")
         del b[n:]
-        return bytes(b)
+        return b.take_bytes()
 
     def readall(self):
         """Read until EOF, using multiple read() call."""
@@ -628,7 +628,7 @@ def readall(self):
         while data := self.read(DEFAULT_BUFFER_SIZE):
             res += data
         if res:
-            return bytes(res)
+            return res.take_bytes()
         else:
             # b'' or None
             return data
@@ -1738,7 +1738,7 @@ def readall(self):
         assert len(result) - bytes_read >= 1, \
             "os.readinto buffer size 0 will result in erroneous EOF / returns 0"
         result.resize(bytes_read)
-        return bytes(result)
+        return result.take_bytes()
 
     def readinto(self, buffer):
         """Same as RawIOBase.readinto()."""