[build] Split pyodide repos from Python deps file

[ryanking13]

This is a QOL improvements that splits out the Pyodide dependencies from the python.MODULE.bazel file into pyodide.MODULE.bazel. This allows our internal repo to symlink this file instead of updating two different files at the same time when we e.g. update Pyodide bundles or memory snapshots.

[ask-bonk]

The use_repo lists match exactly. This is a clean, mechanical split. The changes are:

1. MODULE.bazel: Adds include("//build/deps:pyodide.MODULE.bazel") after the python.MODULE.bazel include.
2. build/deps/pyodide.MODULE.bazel (new): Contains the use_extension + use_repo block that was previously in python.MODULE.bazel, pointing at the new pyodide.bzl extension.
3. build/deps/pyodide.bzl (new): Contains the module_extension definition that was previously at the bottom of dep_pyodide.bzl, loading dep_pyodide from the existing file.
4. build/deps/dep_pyodide.bzl: Removes the old module_extension definition (moved to pyodide.bzl).
5. build/deps/python.MODULE.bazel: Removes the pyodide use_extension + use_repo block (moved to pyodide.MODULE.bazel).

No logic changed. The dep_pyodide() function is untouched. The repo list is identical. The refactoring is purely organizational.

LGTM

github run

[dom96]

Beautiful! I love it. Thank you.