Provide a simpler way to build a nested series from a collection of dataframes

[hombit]

Feature request

Currently, nested_series.apply(lambda x: x) outputs a new series with object dtype. It would be nice if we'd provide a simple way to convert it back to nested series.

Options:

# 1. Does it already work?
nested_series[:] = nested_series.apply(lambda x: x)

# 2. Converter function
df["nested"] = pack_dfs(df["nested"].apply(lambda x: x))

# 3. Patch NestedFrame.__setitem__ to make the magic so this would work
df["nested"] = df["nested"].apply(lambda x: x)

# 4. Patch NestedFrame.apply to make the magic so this would work
df["nested"] = df["nested"].apply(lambda x: x)

# 5. Add kwarg to NestedFrame.apply(output_is_nested=False)
df["nested"] = df["nested"].apply(lambda x: x, output_is_nested=True)

Before submitting
Please check the following:

• I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
• I have included any relevant links, screenshots, environment information, and data relevant to implementing the requested feature, as well as pseudocode for how I want to access the new functionality.
• If I have ideas for how the new feature could be implemented, I have provided explanations and/or pseudocode and/or task lists for the steps.