Improved documentation in service.hpp, fixed compiler warnings

The comments on the main API functions in service.hpp were missing some
details and were sometimes out-of-date with respect to the code. Also,
a newer g++ (version 13.3) emitted some warnings about existing code
that needed to be updated (e.g. to remove unnecessary std::moves).
Finally, the string constants in service.hpp should be declared as
constexpr strings, not macros, to match Derecho's usage of these types
of constants for Conf strings.

Author: etremel

include/cascade/detail/service_impl.hpp

@@ -2440,7 +2440,7 @@ void ExecutionEngine<CascadeTypes...>::workhorse(uint32_t worker_id, struct acti
     dbg_default_trace("Cascade context workhorse[{}] started", worker_id);
     while(is_running) {
         // waiting for an action
-        Action action = std::move(aq.action_buffer_dequeue(is_running));
+        Action action = aq.action_buffer_dequeue(is_running);
         // if action_buffer_dequeue return with is_running == false, value_ptr is invalid(nullptr).
         action.fire(this,worker_id);