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

# non-native
# setup: import matplotlib ; import numpy as np ; matplotlib.use('module://matplotlib_pyodide.wasm_backend') ; from matplotlib import pyplot as plt ;
# run: wasm_custom_font()

# pythran export wasm_custom_font()
import matplotlib
import numpy as np

matplotlib.use("module://matplotlib_pyodide.wasm_backend")
from matplotlib import pyplot as plt  # noqa: E402


def wasm_custom_font():
    f = {"fontname": "cmsy10"}
    t = np.arange(0.0, 2.0, 0.01)
    s = 1 + np.sin(2 * np.pi * t)
    plt.figure()
    plt.title("A simple Sine Curve", **f)
    plt.plot(t, s, linewidth=1.0, marker=11)
    plt.plot(t, t)
    plt.grid(True)
    plt.show()
    plt.close("all")
    plt.clf()

# non-native
# setup: import matplotlib ; import numpy as np ; matplotlib.use('module://matplotlib_pyodide.wasm_backend') ; from matplotlib import pyplot as plt ;
# run: wasm_custom_font()

# pythran export wasm_custom_font()
import matplotlib
import numpy as np

matplotlib.use("module://matplotlib_pyodide.wasm_backend")
from matplotlib import pyplot as plt  # noqa: E402


def wasm_custom_font():
    f = {"fontname": "cmsy10"}
    t = np.arange(0.0, 2.0, 0.01)
    s = 1 + np.sin(2 * np.pi * t)
    plt.figure()
    plt.title("A simple Sine Curve", **f)
    plt.plot(t, s, linewidth=1.0, marker=11)
    plt.plot(t, t)
    plt.grid(True)
    plt.show()
    plt.close("all")
    plt.clf()
