Thanks for the PR! LGTM - one comment

I've added a using declaration to differentiate logically between a string_t and a bitstring_t so we know what the argument is supposed to represent

But in the future we should probably do this:

struct bitstring_t : public string_t { // NOLINT
};

(this is also what we do for the timestamp variants)

struct timestamp_tz_t : public timestamp_t { // NOLINT
};
struct timestamp_ns_t : public timestamp_t { // NOLINT
};
struct timestamp_ms_t : public timestamp_t { // NOLINT
};
struct timestamp_sec_t : public timestamp_t { // NOLINT
};

So this differentiation is explicit at the type system level, while still sharing the same underlying physical representation

Thanks! Good idea to create the separate type.