Merge pyodide_py into python_stdlib.zip. ### Description

Merges pyodide_py.tar into python_stdlib.zip. This reduces the number of network requests during the initialization.

The original intention of splitting pyodide_py.tar from pyodide.asm.data was to give users an option to provide custom files (#2023), which is now available by modifying python_stdlib.zip directly. So I think there is no reason to have both python_stdlib.zip and pyodide_py.tar.

### Checklists

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests

# setup: import pandas as pd ; import numpy ; N = 1000000 ; df1 = pd.DataFrame(numpy.random.randint(0, 10, size=(N, 3)), columns=["col1", "col2", "col3"]) ; df2 = pd.DataFrame(numpy.random.randint(0, 10, size=(N, 3)), columns=["col4", "col5", "col6"])
# run: join_df(df1, df2)


def join_df(df1, df2):
    return df1.join(df2, how="outer")

# setup: import pandas as pd ; import numpy ; N = 1000000 ; df1 = pd.DataFrame(numpy.random.randint(0, 10, size=(N, 3)), columns=["col1", "col2", "col3"]) ; df2 = pd.DataFrame(numpy.random.randint(0, 10, size=(N, 3)), columns=["col4", "col5", "col6"])
# run: join_df(df1, df2)


def join_df(df1, df2):
    return df1.join(df2, how="outer")
