~~Isn't the handling of `endptr` incorrect in `DYN_ARR_RESET` as well? `a.endptr = a.data;` feels very incorrect to me.~~ Nevermind, I see how it's supposed to

~~Isn't the handling of `endptr` incorrect in `DYN_ARR_RESET` as well? `a.endptr = a.data;` feels very incorrect to me.~~ Nevermind, I see how it's supposed to work now. To your point, `RESIZE` is definitely incorrect. It should be checking the length before calling `realloc`.