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

def test_pytest(selenium):
    # TODO: don't use numpy in this test as it's not necessarily installed.
    selenium.load_package(["pytest", "numpy", "nose"])

    selenium.run(
        """
        from pathlib import Path
        import os
        import numpy
        import pytest

        base_dir = Path(numpy.__file__).parent / "core" / "tests"
        """
    )

    selenium.run("pytest.main([str(base_dir / 'test_api.py')])")

    logs = "\n".join(selenium.logs)
    assert "INTERNALERROR" not in logs

def test_pytest(selenium):
    # TODO: don't use numpy in this test as it's not necessarily installed.
    selenium.load_package(["pytest", "numpy", "nose"])

    selenium.run(
        """
        from pathlib import Path
        import os
        import numpy
        import pytest

        base_dir = Path(numpy.__file__).parent / "core" / "tests"
        """
    )

    selenium.run("pytest.main([str(base_dir / 'test_api.py')])")

    logs = "\n".join(selenium.logs)
    assert "INTERNALERROR" not in logs
