Use bracketed paste to escape newlines and tabs properly

[jishnusen]

Uses escape chars to properly insert multiline strings. This prevents REPLs like ipython from modifying the inserted buffer in undefined ways. See: https://github.com/jpalardy/vim-slime/blob/a532203bcd7af7f5e571c07b60bba7287076dc19/doc/vim-slime.txt#L124C2-L124C38