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 random ; TESTDATA = "col1;col2;col3\n" + "\n".join(";".join(map(str, [random.randint(0, 1) for _ in range(3)])) + "\n" for _ in range(10000))
# run: read_csv(TESTDATA)

from io import StringIO

import pandas as pd


def read_csv(data):
    return pd.read_csv(StringIO(data), sep=";")

# setup: import random ; TESTDATA = "col1;col2;col3\n" + "\n".join(";".join(map(str, [random.randint(0, 1) for _ in range(3)])) + "\n" for _ in range(10000))
# run: read_csv(TESTDATA)

from io import StringIO

import pandas as pd


def read_csv(data):
    return pd.read_csv(StringIO(data), sep=";")
