Objects which can be converted to and from Bigstring.t. The following holds for all modules implementing this interface.
(to_bigstring (of_bigstring (to_bigstring t)) = to_bigstring t
If the object also implements Stringable, the following should hold:
Bigstring.to_string (to_bigstring t) = to_string t
Creates an object of type t from a Bigstring.t. The source Bigstring might not be copied, so it should be copied if the need to mutate it arises. The latter does not apply if the implementation of to_bigstring explicitly says that this is unnecessary.