byteArrayToByteString, and byteStringToByteArray?

i find myself using the following more often now:

```haskell
unsafeByteArrayToByteString :: ByteArray -> ByteString
unsafeByteArrayToByteString (ByteArray b#) =
let addr# = byteArrayContents# b#
fp = ForeignPtr addr# (PlainPtr (unsafeCoerce# b#))
len = I# (sizeofByteArray# b#)
in PS fp 0 len

byteArrayToByteString :: ByteArray -> ByteString
byteArrayToByteString b@(ByteArray b#)
| isTrue# (isByteArrayPinned# b#) = unsafeByteArrayToByteString b
| otherwise = runST $ do
let len = sizeofByteArray b
marr@(MutableByteArray marr#) <- newPinnedByteArray len
copyByteArray marr 0 b 0 len
let addr# = byteArrayContents# (unsafeCoerce# marr#)
let fp = ForeignPtr addr# (PlainPtr (unsafeCoerce# marr#))
pure (PS fp 0 len)

byteStringToByteArray :: ByteString -> ByteArray
byteStringToByteArray (PS fp off len) =
accursedUnutterablePerformIO $
withForeignPtr fp $ \ptr -> do
marr <- newByteArray len
copyPtrToMutableByteArray (ptr `plusPtr` off) marr 0 len
unsafeFreezeByteArray marr
```

is it possible that these could be added somewhere? i work with ByteArray a lot more than i do bytestring, but there are places where ByteString is necessary because of other apis (aeson, binary, etc.)