Merge pull request #26875 from asmorkalov:as/in_memory_models

Added trackers factory with pre-loaded dnn models #26875

Replaces https://github.com/opencv/opencv/pull/26295

Allows to substitute custom models or initialize tracker from in-memory model.

### 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
- [ ] The PR is proposed to the proper branch
- [ ] 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/python/test/tests_common.py

@@ -24,11 +24,12 @@ class NewOpenCVTests(unittest.TestCase):
     # path to local repository folder containing 'samples' folder
     repoPath = None
     extraTestDataPath = None
+    extraDnnTestDataPath = None
     # github repository url
     repoUrl = 'https://raw.github.com/opencv/opencv/4.x'
 
     def find_file(self, filename, searchPaths=[], required=True):
-        searchPaths = searchPaths if searchPaths else [self.repoPath, self.extraTestDataPath]
+        searchPaths = searchPaths if searchPaths else [self.repoPath, self.extraTestDataPath, self.extraDnnTestDataPath]
         for path in searchPaths:
             if path is not None:
                 candidate = path + '/' + filename
@@ -83,10 +84,17 @@ class NewOpenCVTests(unittest.TestCase):
         print("Testing OpenCV", cv.__version__)
         print("Local repo path:", args.repo)
         NewOpenCVTests.repoPath = args.repo
+
         try:
             NewOpenCVTests.extraTestDataPath = os.environ['OPENCV_TEST_DATA_PATH']
         except KeyError:
             print('Missing opencv extra repository. Some of tests may fail.')
+
+        try:
+            NewOpenCVTests.extraDnnTestDataPath = os.environ['OPENCV_DNN_TEST_DATA_PATH']
+        except KeyError:
+            pass
+
         random.seed(0)
         unit_argv = [sys.argv[0]] + other
         unittest.main(argv=unit_argv)