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/lib/engine/engine_graph.cpp

@@ -900,7 +900,6 @@ namespace gridfire {
         const double rho,
         const SparsityPattern &sparsityPattern
     ) const {
-        //TODO: The issue now seems to be that the jacobian is returning all zeros. I need to sort out why this is
         SparsityPattern intersectionSparsityPattern;
         for (const auto& entry : sparsityPattern) {
             if (m_full_sparsity_set.contains(entry)) {

src/lib/reaction/reaction.cpp

@@ -417,6 +417,13 @@ namespace gridfire::reaction {
         }
     }
 
+    std::optional<std::unique_ptr<Reaction>> ReactionSet::get(const std::string_view &id) const {
+        if (!contains(id)) {
+            return std::nullopt;
+        }
+        return std::make_optional(m_reactions[m_reactionNameMap.at(std::string(id))]->clone());
+    }
+
     void ReactionSet::remove_reaction(const Reaction& reaction) {
         const auto reaction_id = std::string(reaction.id());
         if (!m_reactionNameMap.contains(reaction_id)) {