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

from pytest_pyodide import run_in_pyodide


@run_in_pyodide(packages=["test", "lzma"], pytest_assert_rewrites=False)
def test_lzma(selenium):
    # TODO: libregrtest.main(["test_lzma"]) doesn't collect any tests for some unknown reason.

    import test.test_lzma
    import unittest

    suite = unittest.TestSuite(
        [unittest.TestLoader().loadTestsFromModule(test.test_lzma)]
    )

    runner = unittest.TextTestRunner(verbosity=2)
    result = runner.run(suite)
    assert result.wasSuccessful()

from pytest_pyodide import run_in_pyodide


@run_in_pyodide(packages=["test", "lzma"], pytest_assert_rewrites=False)
def test_lzma(selenium):
    # TODO: libregrtest.main(["test_lzma"]) doesn't collect any tests for some unknown reason.

    import test.test_lzma
    import unittest

    suite = unittest.TestSuite(
        [unittest.TestLoader().loadTestsFromModule(test.test_lzma)]
    )

    runner = unittest.TextTestRunner(verbosity=2)
    result = runner.run(suite)
    assert result.wasSuccessful()
