Lock prompt in interpreter

I dont like how we are able to traverse the prompt in Interactive Mode.
`ƛ>` This part of the interpreter should only be readable and not selectable. The current behavior is such that in insert mode you can go to the left of the prompt and this causes headaches. For reference solution see Python's interactive mode, they handle the prompt perfectly. The outcome of the current faulty behavior is that if you `dd` a line in the interactive ghci, you won't be able to delete the line because the prompt is treated as the part of the input

Start by reproducing the issue in an interactive GHCi session through haskell-mode: test moving left of the `ƛ>` prompt in insert mode and deleting a line with `dd`. Locate the prompt-handling code, compare the behavior with Python's interactive mode, and consider the issue done when the prompt is readable but not selectable and input lines can be deleted normally.

Written by the indexing model from the issue text.