Address review comments on the simdutf backend

string_bulk_run() had the same `return scalar_string_bulk_run(...)` in both
arms of the `#if`. The simdutf arm already falls through when validation
fails, so a single return after the `#endif` says the same thing.

The JSON_USE_SIMDUTF example showed `#include <simdutf.h>`, which
string_scan.hpp already does under the same guard; users only have to put the
header on the include path and link the library, not include it themselves.

Set the version history entry to 3.13.0, matching the other macro pages
documenting unreleased features.

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MXDi7NTMKAmoArUZSKMc4T
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/macros/json_use_simdutf.md

@@ -41,7 +41,6 @@ By default, `#!cpp JSON_USE_SIMDUTF` is not defined and the portable C++11 scala
 
     ```cpp
     #define JSON_USE_SIMDUTF 1
-    #include <simdutf.h>
     #include <nlohmann/json.hpp>
 
     ...
@@ -56,4 +55,4 @@ By default, `#!cpp JSON_USE_SIMDUTF` is not defined and the portable C++11 scala
 
 ## Version history
 
-- Added in version 3.12.1.
+- Added in version 3.13.0.

include/nlohmann/detail/input/string_scan.hpp

@@ -227,10 +227,8 @@ inline std::size_t string_bulk_run(const unsigned char* data, std::size_t n) noe
     {
         return run;
     }
-    return scalar_string_bulk_run(data, n);
-#else
-    return scalar_string_bulk_run(data, n);
 #endif
+    return scalar_string_bulk_run(data, n);
 }
 
 }  // namespace detail

single_include/nlohmann/json.hpp

@@ -8360,10 +8360,8 @@ inline std::size_t string_bulk_run(const unsigned char* data, std::size_t n) noe
     {
         return run;
     }
-    return scalar_string_bulk_run(data, n);
-#else
-    return scalar_string_bulk_run(data, n);
 #endif
+    return scalar_string_bulk_run(data, n);
 }
 
 }  // namespace detail