Merge pull request #28967 from IbrahimNamdari:add-video-context-manager

Python: add context manager compatibility for VideoCapture and VideoWriter #28967

### Description
This PR implements the context manager protocol (`with` statement support) for `cv2.VideoCapture` and `cv2.VideoWriter` objects in Python.

### Problem
Currently, these classes do not support the context manager protocol, leading to a `TypeError: ... object does not support the context manager protocol` when used with a `with` block. As reported in issue #28956, if an exception occurs before an explicit `.release()` call, the video resource or file remains locked in the system[cite: 298, 309].

### Identification & Motivation
By analyzing the issue and the Python binding structure of OpenCV, I identified that while the core logic resides in C++, the Pythonic behavior can be enhanced by injecting `__enter__` and `__exit__` methods during the module initialization. This ensures that resources are automatically and safely released even if the program execution is interrupted by an error[cite: 298, 325].

### Solution
I have modified `modules/python/package/cv2/__init__.py` to dynamically inject the necessary methods:
1. Defined `_video_enter` to return the object itself (standard context manager behavior).
2. Defined `_video_exit` to trigger the `.release()` method automatically.
3. Injected these methods into `VideoCapture` and `VideoWriter` classes immediately after the `bootstrap()` function to ensure the native C++ classes are correctly loaded into the global namespace.

Fixes #28956

modules/videoio/misc/python/pyopencv_videoio.hpp

@@ -141,4 +141,34 @@ bool pyopencv_to(PyObject* obj, Ptr<cv::IStreamReader>& p, const ArgInfo&)
     return false;
 }
 
+static PyObject* pycvVideoEnter(PyObject* self, PyObject* /*args*/, PyObject* /*kw*/) {
+    Py_INCREF(self);
+    return self;
+}
+
+static PyObject* pycvVideoCaptureExit(PyObject* self, PyObject* /*args*/, PyObject* /*kw*/) {
+    Ptr<cv::VideoCapture>* obj_getp = nullptr;
+    if (pyopencv_VideoCapture_getp(self, obj_getp) && obj_getp && *obj_getp) {
+        (*obj_getp)->release();
+    }
+    Py_RETURN_NONE;
+}
+
+static PyObject* pycvVideoWriterExit(PyObject* self, PyObject* /*args*/, PyObject* /*kw*/) {
+    Ptr<cv::VideoWriter>* obj_getp = nullptr;
+    if (pyopencv_VideoWriter_getp(self, obj_getp) && obj_getp && *obj_getp) {
+        (*obj_getp)->release();
+    }
+    Py_RETURN_NONE;
+}
+
+#define PYOPENCV_EXTRA_METHODS_VideoCapture \
+    {"__enter__", CV_PY_FN_WITH_KW(pycvVideoEnter), "Context manager enter"}, \
+    {"__exit__",  CV_PY_FN_WITH_KW(pycvVideoCaptureExit), "Context manager exit"},
+
+#define PYOPENCV_EXTRA_METHODS_VideoWriter \
+    {"__enter__", CV_PY_FN_WITH_KW(pycvVideoEnter), "Context manager enter"}, \
+    {"__exit__",  CV_PY_FN_WITH_KW(pycvVideoWriterExit), "Context manager exit"},
+
+
 #endif // HAVE_OPENCV_VIDEOIO