build(GridFire): building on gcc and clang

resolved some issues preventing GridFire from building on both gcc and clang. Also resolved all warnings on both compilers.

src/include/gridfire/reaction/reaclib.h

@@ -4,7 +4,7 @@
 
 namespace gridfire::reaclib {
 
-    static bool s_initialized = false;
+    [[maybe_unused]] static bool s_initialized = false;
 
     /**
      * @brief Provides global access to the fully initialized REACLIB reaction set.

src/include/gridfire/reaction/reaction.h

@@ -536,7 +536,7 @@ namespace gridfire::reaction {
         ///
         friend std::ostream& operator<<(std::ostream& os, const TemplatedReactionSet<ReactionT>& r) {
             os << "(ReactionSet: [";
-            int counter = 0;
+            size_t counter = 0;
             for (const auto& reaction : r.m_reactions) {
                 os << reaction;
                 if (counter < r.m_reactions.size() - 2) {