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

import pytest


@pytest.mark.driver_timeout(40)
def test_pyb2d(selenium_standalone, request):
    selenium = selenium_standalone
    selenium.load_package("pyb2d")

    selenium.run(
        """
        import numpy as np
        import b2d
        w = b2d.world(gravity=(0,-10))
        """
    )

import pytest


@pytest.mark.driver_timeout(40)
def test_pyb2d(selenium_standalone, request):
    selenium = selenium_standalone
    selenium.load_package("pyb2d")

    selenium.run(
        """
        import numpy as np
        import b2d
        w = b2d.world(gravity=(0,-10))
        """
    )
