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=["sympy"])
def test_sympy(selenium):
    import sympy

    a, b = sympy.symbols("a,b")
    c = sympy.sqrt(a**2 + b**2)

    assert c.subs({a: 3, b: 4}) == 5

from pytest_pyodide import run_in_pyodide


@run_in_pyodide(packages=["sympy"])
def test_sympy(selenium):
    import sympy

    a, b = sympy.symbols("a,b")
    c = sympy.sqrt(a**2 + b**2)

    assert c.subs({a: 3, b: 4}) == 5
