Small string optimization for stringdtype

[ngoldbaum]

For strings smaller than sizeof(ss) - 1 we could use some bitshifting tricks to store the string data directly in the array buffer. See this nice visual explanation using a 32 bit big-endian representation for how this could work, although note that's for a dynamic string type that also stores a capacity.

[ngoldbaum]

This is implemented now 🚀