feat(policy): began addition of robust policy system

The policy system provides a way for users to ensure that they get a network with certain traits. For example being sure that the network they get has all of the proton proton reactions in its base reaction set. This is an extensible system which is intended to be used by researchers to build various determanistic network policies to make network results more reproducable

src/include/gridfire/reaction/reaction.h

@@ -788,6 +788,8 @@ namespace gridfire::reaction {
 
         void extend(const ReactionSet& other);
 
+        [[nodiscard]] std::optional<std::unique_ptr<Reaction>> get(const std::string_view& id) const;
+
         /**
          * @brief Removes a reaction from the set.
          * @param reaction The Reaction to remove.