Fix gcc-12 -Wmicrosoft-cast warning in trace_sink_impl

Explicitly convert function pointer to std::uintptr_t in write_pf() instead of
relying on implicit conversion through operator<<. This avoids the -Wmicrosoft-cast
warning while using the same reinterpret_cast approach that ostdstream.hpp already
uses for function pointer output.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jll63

include/boost/openmethod/initialize.hpp

@@ -10,6 +10,7 @@
 #include <boost/openmethod/detail/ostdstream.hpp>
 
 #include <algorithm>
+#include <charconv>
 #include <cstdint>
 #include <deque>
 #include <map>
@@ -166,7 +167,14 @@ struct trace_sink_impl : trace_sink {
 
     void write_pf(void (*value)()) override {
         if constexpr (Registry::has_output) {
-            Registry::output::stream() << value;
+            // Explicit conversion to avoid -Wmicrosoft-cast warning on
+            // implicit function-pointer to void-pointer conversion
+            std::array<char, 20> str;
+            auto end = std::to_chars(
+                           str.data(), str.data() + str.size(),
+                           reinterpret_cast<std::uintptr_t>(value), 16)
+                           .ptr;
+            Registry::output::stream() << std::string_view(str.data(), end - str.data());
         }
     }