Merge pull request #26434 from dkurt:dk/int64_file_storage_4.x

int64 data type support for FileStorage. 1d and empty Mat with exact dimensions #26434

### Pull Request Readiness Checklist

Port of https://github.com/opencv/opencv/pull/26399 to 4.x branch

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/core/src/persistence_xml.cpp

@@ -145,6 +145,12 @@ public:
         writeScalar( key, ptr);
     }
 
+    void write(const char* key, int64_t value)
+    {
+        char buf[128], *ptr = fs::itoa( value, buf, 10, true );
+        writeScalar( key, ptr);
+    }
+
     void write( const char* key, double value )
     {
         char buf[128];
@@ -556,7 +562,7 @@ public:
                     }
                     else
                     {
-                        int ival = (int)strtol( ptr, &endptr, 0 );
+                        int64_t ival = strtoll( ptr, &endptr, 0 );
                         elem->setValue(FileNode::INT, &ival);
                     }