fix: use std::to_chars instead of std::format

src/coyote.cpp

 #include <cassert>
+#include <charconv>
 #include <coyote.hpp>
-#include <format>
 #include <iostream>
 #include <memory>
 #include <numeric>
@@ -58,9 +58,10 @@ namespace coyote {
 
             size_t hash = std::hash<std::string>{}(
                 iso_dt.value() + std::to_string(yac_time_reduction) + interpolation_stack_yaml);
-            std::string tgt_field_name =
-                "target:" + source_field + "(" + std::format("{:x}", hash) + ")";
-            int target_field_id = -1;
+            char hash_str[2 * sizeof(hash)];
+            std::to_chars(hash_str, hash_str + (2 * sizeof(hash)), hash, 16);
+            std::string tgt_field_name = "target:" + source_field + "(" + hash_str + ")";
+            int target_field_id        = -1;
             yac_cdef_field(
                 tgt_field_name.c_str(),
                 _yac_comp_id,