Enhance OpenCVCamera with FOURCC for MJPEG support and validation (#1558)

* Enhance OpenCVCamera with FOURCC support and validation

- Added FOURCC configuration option to OpenCVCamera and OpenCVCameraConfig for specifying video format.
- Implemented _validate_fourcc method to validate and set the camera's FOURCC code.
- Updated _configure_capture_settings to apply FOURCC settings before FPS and resolution.
- Enhanced camera detection to include default FOURCC code in camera info.
- Updated documentation to reflect new FOURCC parameter and its implications on performance.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Add tests for FOURCC configuration in OpenCVCamera

- Implemented tests to validate FOURCC configuration and its application in OpenCVCamera.
- Added checks for valid FOURCC codes and ensured that invalid codes raise appropriate errors.
- Included a test for camera connection functionality using specified FOURCC settings.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix circular import in __init__.py - change to relative import

* Update src/lerobot/cameras/opencv/configuration_opencv.py

Co-authored-by: Steven Palma <imstevenpmwork@ieee.org>
Signed-off-by: hls <56255627+forgetwhatuwant@users.noreply.github.com>

* Update src/lerobot/cameras/opencv/configuration_opencv.py

Co-authored-by: Steven Palma <imstevenpmwork@ieee.org>
Signed-off-by: hls <56255627+forgetwhatuwant@users.noreply.github.com>

* fix(camera_opencv): ensure MSMF hardware transform compatibility on Windows before importing OpenCV

* This change reverts the import from a relative import (.) back to the absolute import (lerobot.) as it was previously

* opencv/config: satisfy Ruff SIM102 by merging nested if for fourcc validation

* style(opencv/config): apply ruff-format changes

---------

Signed-off-by: hls <56255627+forgetwhatuwant@users.noreply.github.com>
Signed-off-by: Steven Palma <imstevenpmwork@ieee.org>
Co-authored-by: forgetwhatuwant <forgetwhatuwant@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Steven Palma <imstevenpmwork@ieee.org>

tests/cameras/test_opencv.py

@@ -155,6 +155,46 @@ def test_async_read_before_connect():
         _ = camera.async_read()
 
 
+def test_fourcc_configuration():
+    """Test FourCC configuration validation and application."""
+
+    # Test MJPG specifically (main use case)
+    config = OpenCVCameraConfig(index_or_path=DEFAULT_PNG_FILE_PATH, fourcc="MJPG")
+    camera = OpenCVCamera(config)
+    assert camera.config.fourcc == "MJPG"
+
+    # Test a few other common formats
+    valid_fourcc_codes = ["YUYV", "YUY2", "RGB3"]
+
+    for fourcc in valid_fourcc_codes:
+        config = OpenCVCameraConfig(index_or_path=DEFAULT_PNG_FILE_PATH, fourcc=fourcc)
+        camera = OpenCVCamera(config)
+        assert camera.config.fourcc == fourcc
+
+    # Test invalid FOURCC codes
+    invalid_fourcc_codes = ["ABC", "ABCDE", ""]
+
+    for fourcc in invalid_fourcc_codes:
+        with pytest.raises(ValueError):
+            OpenCVCameraConfig(index_or_path=DEFAULT_PNG_FILE_PATH, fourcc=fourcc)
+
+
+def test_fourcc_with_camera():
+    """Test FourCC functionality with actual camera connection."""
+    config = OpenCVCameraConfig(index_or_path=DEFAULT_PNG_FILE_PATH, fourcc="MJPG")
+    camera = OpenCVCamera(config)
+
+    # Connect should work with MJPG specified
+    camera.connect(warmup=False)
+    assert camera.is_connected
+
+    # Read should work normally
+    img = camera.read()
+    assert isinstance(img, np.ndarray)
+
+    camera.disconnect()
+
+
 @pytest.mark.parametrize("index_or_path", TEST_IMAGE_PATHS, ids=TEST_IMAGE_SIZES)
 @pytest.mark.parametrize(
     "rotation",