Un-nest the run-length ternary in the string escaper

clang-tidy's readability-avoid-nested-conditional-operator (newly enforced
by the ci_clang_tidy job's clang) rejected the nested ?: that picked the
run length: EnsureAscii ? (is_ascii_copyable(...) ? scan : 0) : bulk.

Compute it in an immediately-invoked lambda instead. The value stays const
and the laziness is unchanged - the ascii scan still runs only on the
ensure_ascii path when the first byte is copyable, and string_bulk_run only
on the other path (EnsureAscii is a template bool, so the dead branch is
folded away). Output is byte-for-byte identical; single_include regenerated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L1oJ2ggRHS37zeVe94QTA1
Signed-off-by: Claude <noreply@anthropic.com>

include/nlohmann/detail/output/serializer.hpp

@@ -850,11 +850,16 @@ class serializer
                 // for the scan. Without it, text whose characters all have to be
                 // escaped - CJK under ensure_ascii, where every byte is >= 0x80 -
                 // runs the scanner once per character only to be told zero.
-                const std::size_t run = EnsureAscii
-                                        ? (is_ascii_copyable(data[i])
-                                           ? find_ascii_copyable_run(data + i, s.size() - i)
-                                           : 0)
-                                        : string_bulk_run(data + i, s.size() - i);
+                const std::size_t run = [&]() -> std::size_t
+                {
+                    if (EnsureAscii)
+                    {
+                        return is_ascii_copyable(data[i])
+                        ? find_ascii_copyable_run(data + i, s.size() - i)
+                        : 0;
+                    }
+                    return string_bulk_run(data + i, s.size() - i);
+                }();
                 if (run != 0)
                 {
                     // emit any bytes still pending in string_buffer first to

single_include/nlohmann/json.hpp

@@ -21910,11 +21910,16 @@ class serializer
                 // for the scan. Without it, text whose characters all have to be
                 // escaped - CJK under ensure_ascii, where every byte is >= 0x80 -
                 // runs the scanner once per character only to be told zero.
-                const std::size_t run = EnsureAscii
-                                        ? (is_ascii_copyable(data[i])
-                                           ? find_ascii_copyable_run(data + i, s.size() - i)
-                                           : 0)
-                                        : string_bulk_run(data + i, s.size() - i);
+                const std::size_t run = [&]() -> std::size_t
+                {
+                    if (EnsureAscii)
+                    {
+                        return is_ascii_copyable(data[i])
+                        ? find_ascii_copyable_run(data + i, s.size() - i)
+                        : 0;
+                    }
+                    return string_bulk_run(data + i, s.size() - i);
+                }();
                 if (run != 0)
                 {
                     // emit any bytes still pending in string_buffer first to