Use std::char_traits<char>::length instead of strlen in dump_float()

Codacy (flawfinder, CWE-126) flags strlen on the locale's decimal point.
The string is NUL-terminated by localeconv(), so the behavior is the same.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N5NasAgbDGG28MqXjQvLqp
Signed-off-by: Claude <noreply@anthropic.com>

include/nlohmann/detail/output/serializer.hpp

@@ -15,7 +15,7 @@
 #include <cstddef> // size_t, ptrdiff_t
 #include <cstdint> // uint8_t
 #include <cstdio> // snprintf
-#include <cstring> // memcpy, memset, strlen
+#include <cstring> // memcpy, memset
 #include <iterator> // next
 #include <limits> // numeric_limits
 #include <string> // string, char_traits
@@ -2102,7 +2102,7 @@ class serializer
         const auto* loc = std::localeconv();
         JSON_ASSERT(loc != nullptr);
         const char* const decimal_point = (loc->decimal_point == nullptr) ? "" : loc->decimal_point;
-        const std::size_t decimal_point_len = std::strlen(decimal_point);
+        const std::size_t decimal_point_len = std::char_traits<char>::length(decimal_point);
 
         // convert decimal point to '.'
         if (decimal_point_len != 0 && !(decimal_point_len == 1 && decimal_point[0] == '.'))