Merge pull request #26849 from sturkmen72:apng-writeanimation

APNG encoding optimization #26849

related #26840

### Pull Request Readiness Checklist

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
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/imgcodecs/test/test_animation.cpp

@@ -3,31 +3,10 @@
 // of this distribution and at http://opencv.org/license.html.
 
 #include "test_precomp.hpp"
+#include "test_common.hpp"
 
 namespace opencv_test { namespace {
 
-static void readFileBytes(const std::string& fname, std::vector<unsigned char>& buf)
-{
-    FILE * wfile = fopen(fname.c_str(), "rb");
-    if (wfile != NULL)
-    {
-        fseek(wfile, 0, SEEK_END);
-        size_t wfile_size = ftell(wfile);
-        fseek(wfile, 0, SEEK_SET);
-
-        buf.resize(wfile_size);
-
-        size_t data_size = fread(&buf[0], 1, wfile_size, wfile);
-
-        if(wfile)
-        {
-            fclose(wfile);
-        }
-
-        EXPECT_EQ(data_size, wfile_size);
-    }
-}
-
 static bool fillFrames(Animation& animation, bool hasAlpha, int n = 14)
 {
     // Set the path to the test image directory and filename for loading.