Make explicit buffering easier when using `withFile`

I had a bug where my output file was always empty. I tracked it down to the default buffering mode. I think it would be better offer a variant of `withFile` that explicitly specifies the buffering mode.

What do you think?

```
withFile' :: MonadSafe m => FilePath -> IO.IOMode -> IO.BufferMode -> (IO.Handle -> m r) -> m r
withFile' file ioMode bufferMode = PS.bracket
(liftIO $ do
h <- IO.openFile file ioMode
IO.hSetBuffering h bufferMode
pure h)
(liftIO . IO.hClose)
```

Start by locating the existing withFile entry point and checking how it opens and closes handles. Compare its behavior with the proposed withFile' signature and verify that explicit IO.BufferMode settings are applied correctly; done means callers can choose buffering without losing safe resource cleanup.

Written by the indexing model from the issue text.