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/test/test_io.cpp

@@ -2003,4 +2003,33 @@ TEST(Core_InputOutput, FileStorage_invalid_attribute_value_regression_25946)
     ASSERT_EQ(0, std::remove(fileName.c_str()));
 }
 
+template <typename T>
+T fsWriteRead(const T& expectedValue, const char* ext)
+{
+    std::string fname = cv::tempfile(ext);
+    FileStorage fs_w(fname, FileStorage::WRITE);
+    fs_w << "value" << expectedValue;
+    fs_w.release();
+
+    FileStorage fs_r(fname, FileStorage::READ);
+
+    T value;
+    fs_r["value"] >> value;
+    return value;
+}
+
+typedef testing::TestWithParam<const char*> FileStorage_exact_type;
+TEST_P(FileStorage_exact_type, long_int)
+{
+    for (const int64_t expected : std::vector<int64_t>{INT64_MAX, INT64_MIN, -1, 1, 0})
+    {
+        int64_t value = fsWriteRead(expected, GetParam());
+        EXPECT_EQ(value, expected);
+    }
+}
+
+INSTANTIATE_TEST_CASE_P(Core_InputOutput,
+    FileStorage_exact_type, Values(".yml", ".xml", ".json")
+);
+
 }} // namespace