CS50R readlines not handled if on multiple lines

[curiouskiwi]

For the checks in CS50R that are dealing with readline prompts (teahouse for example), if the code has split the readline into multiple lines, check50 will produce an error

:| teahouse.R uses readline
    check50 ran into an error while running checks!
    UnboundLocalError: cannot access local variable 'end' where it is not associated with a value
      File "/usr/local/lib/python3.12/site-packages/check50/runner.py", line 148, in wrapper
    state = check(*args)
            ^^^^^^^^^^^^
      File "/home/ubuntu/.local/share/check50/cs50/problems/teahouse/__init__.py", line 18, in readline
    new_contents = replace_readline(contents)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/ubuntu/.local/share/check50/cs50/problems/teahouse/__init__.py", line 93, in replace_readline
    line = line[:start] + f"commandArgs(trailingOnly = TRUE)[{readline_count}]" + line[end + 1:]
                                                                                       ^^

Can be replicated with code like

x <- readline(
    "Prompt: ")

instead of x <-readline("Prompt: ")

[CarterZenke]

Addressed with https://github.com/cs50/problems/commit/1be9de1eec9ccf9a7aab3c6e7bcb3c0905284142. Unfortunately, I don't think it's feasible to reliably find and replace readline if it spans multiple lines—so I've given students a message that they should ensure their usage spans a single line.