Return std::size_t from the hash helper in the ordered_json test

MSVC (Win32) rejected the implicit conversion of the unsigned long long
product to the 32-bit std::size_t (C4244 as an error). Also note when
JSON_NO_THREAD_LOCAL is set in the regression test.

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>

tests/src/unit-ordered_json.cpp

@@ -534,9 +534,10 @@ TEST_CASE("object_key_index")
 
         // the hashes are not distinct on purpose: elements with the same
         // hash are told apart by the caller
-        const auto hash_of = [](std::size_t position)
+        const auto hash_of = [](std::size_t position) -> std::size_t
         {
-            return (position % 50) * 0x9E3779B97F4A7C15ull;
+            // truncated to 32 bits where std::size_t is that small
+            return static_cast<std::size_t>((position % 50) * 0x9E3779B97F4A7C15ull);
         };
 
         std::vector<std::size_t> hashes;

tests/src/unit-regression1.cpp

@@ -1555,6 +1555,7 @@ TEST_CASE("regression tests 1")
         {
             my_json j = make();
 #ifdef JSON_NO_THREAD_LOCAL
+            // (set by the user, or by the library for clang with MinGW)
             // the objects below the outermost one are not copied by their
             // object_t here, but member by member, which keeps their
             // timestamps correct: "c" is not mistaken for "b" and is inserted