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=["lxml"])
def test_lxml(selenium):
    from lxml import etree

    root = etree.XML(
        """<root>
        <TEXT1 class="myitem">one</TEXT1>
        <TEXT2 class="myitem">two</TEXT2>
        <TEXT3 class="myitem">three</TEXT3>
        <v-TEXT4 class="v-list">four</v-TEXT4>
    </root>"""
    )

    items = root.xpath("//*[@class='myitem']")
    assert ["one", "two", "three"] == [item.text for item in items]

from pytest_pyodide import run_in_pyodide


@run_in_pyodide(packages=["lxml"])
def test_lxml(selenium):
    from lxml import etree

    root = etree.XML(
        """<root>
        <TEXT1 class="myitem">one</TEXT1>
        <TEXT2 class="myitem">two</TEXT2>
        <TEXT3 class="myitem">three</TEXT3>
        <v-TEXT4 class="v-list">four</v-TEXT4>
    </root>"""
    )

    items = root.xpath("//*[@class='myitem']")
    assert ["one", "two", "three"] == [item.text for item in items]
