Add `alwayslink = True` to the cc_library used to implement py_extension, otherwise the module init function can be lost.
Add `alwayslink = True` to the cc_library used to implement py_extension,
otherwise the module init function can be lost.

I am not sure why it worked before but it stopped working now.

PiperOrigin-RevId: 276466237

google/riegeli,google/riegeli,google/riegeli,google/riegeli