Support for Multi-line Code Snippets with #@ Marker

[PeterHamfelt]

Steps to reproduce

1. Write a multi-line code snippet (e.g., a Keras Sequential model definition) and place the #@ marker at the end of the line.
2. Try splitting the code across multiple lines while keeping the #@ marker.
3. Run the checker that leverages the #@ marker to see how nodes are created.

Current behavior

The code checker creates new nodes for each line when the #@ marker is used in multi-line code snippets, resulting in separate nodes rather than treating the code block as one unit. This reduces the clarity of scenarios and makes it challenging to handle more complex, multi-line code.

model = tf.keras.Sequential(layers=[
    tf.keras.layers.Dense(units=64, activation='relu'),
    tf.keras.layers.Dense(units=10)
])  #@

Additionally, having everything on a single line makes the code harder to read and maintain. For example, writing it all in one line like below is less readable and too long:

model = tf.keras.Sequential(layers=[tf.keras.layers.Dense(units=64, activation='relu'), tf.keras.layers.Dense(units=10)]) #@

Expected behavior

The code checker should treat multi-line code snippets marked with #@ as a single unit, allowing for improved readability and easier handling of more complex scenarios.

python -c "from astroid import __pkginfo__; print(__pkginfo__.version)" output