refactor(dataset): split LeRobotDataset into DatasetReader & DatasetWriter (+ API cleanup) (#3180)

* refactor(dataset): split reader and writer

* chore(dataset): remove proxys

* refactor(dataset): better reader & writer encapsulation

* refactor(datasets): clean API + reduce leaky implementations

* refactor(dataset): API cleaning for writer, reader and meta

* refactor(dataset): expose writer & reader + other minor improvements

* refactor(dataset): improve teardown routine

* refactor(dataset): add hf_dataset property at the facade level

* chore(dataset): add init for datasset module

* docs(dataset): add docstrings for public API of the dataset classes

* tests(dataset): add tests for new classes

* fix(dataset): remove circular dependecy

tests/datasets/test_image_writer.py

@@ -352,10 +352,14 @@ def test_with_different_image_formats(tmp_path, img_array_factory):
 
 
 def test_safe_stop_image_writer_decorator():
-    class MockDataset:
+    class MockWriter:
         def __init__(self):
             self.image_writer = MagicMock(spec=AsyncImageWriter)
 
+    class MockDataset:
+        def __init__(self):
+            self.writer = MockWriter()
+
     @safe_stop_image_writer
     def function_that_raises_exception(dataset=None):
         raise Exception("Test exception")
@@ -366,7 +370,7 @@ def test_safe_stop_image_writer_decorator():
         function_that_raises_exception(dataset=dataset)
 
     assert str(exc_info.value) == "Test exception"
-    dataset.image_writer.stop.assert_called_once()
+    dataset.writer.image_writer.stop.assert_called_once()
 
 
 def test_main_process_time(tmp_path, img_tensor_factory):