Fix a few ccache cache miss (#2573)

* Fix ccache cache miss

* Do not define _VERSION_ in python bindings

mlx/version.cpp

@@ -1,10 +1,8 @@
 // Copyright © 2025 Apple Inc.
 
-#include <string>
-
 namespace mlx::core {
 
-std::string version() {
+const char* version() {
   return MLX_VERSION;
 }
 

mlx/version.h

@@ -15,6 +15,6 @@ namespace mlx::core {
  *
  * For dev builds, the version will include the suffix ".devYYYYMMDD+hash"
  */
-std::string version();
+const char* version();
 
 } // namespace mlx::core