add functionality required for this test load_collection & collect

add functionality required for this test load_collection & collect

https://github.com/apache/incubator-wayang/blob/1e0f9e8166225176fe3022de5fbcce3dbcba96b9/python/src/pywy/tests/test_decision_tree_regression.py#L23

```python

# limitations under the License.
#

from pywy.dataquanta import WayangContext
from pywy.platforms.java import JavaPlugin
from pywy.platforms.spark import SparkPlugin
import pytest

# TODO: add functionality required for this test load_collection & collect
@pytest.mark.skip(reason="no way of currently testing this, since we are missing implementations for load_collection & collect")
def test_train_and_predict():
# Initialize context with platforms
ctx = WayangContext().register({JavaPlugin, SparkPlugin})

# Input features and labels
features = ctx.load_collection([
[1.0, 2.0],
[2.0, 3.0],
[3.0, 4.0],
[4.0, 5.0]
])
labels = ctx.load_collection([3.0, 4.0, 5.0, 6.0])

# Train the model
model = features.train_decision_tree_regression(labels, max_depth=3, min_instances=1)

# Run predictions on same features
predictions = model.predict(features)

# Collect and validate
result = predictions.collect()
print("Predictions:", result)

assert len(result) is 4, f"Expected len(result) to be 4, but got: {len(result)}"
for pred in result:
assert pred is float
assert pred > 1.0
assert pred <= 7.0

```

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