Observe API C++ SDK

[G4Vi]

Currently the observe api may be used in C++, but requires using raw pointers to pass strings. It would nice to be able to use std::string to pass strings instead.

[nilslice]

could we wrap the C API in a CPP SDK? we know we want to support C, with as few dependencies as possible.

[G4Vi]

The C API is kind of two APIs wrapped into one right now. The imports from dylibso:observe/api that pass strings as ptr and length separately as uint32_ts and the wrappers that take null terminated strings. We'd want to use the former to implement the c++ sdk as the common std::string implementations store the length of the string so it doesn't need to be computed again.