py.typed is in the published wheel but missing from the sdist — source installs lose PEP 561 typing

The published orderedmultidict 1.0.2 wheel contains `orderedmultidict/py.typed`, but a wheel built from the published sdist does not — so anyone installing from source (distros, `--no-binary`, platforms without wheels) silently loses type-checking support.

Fix is one line: ensure `py.typed` is included in the sdist (MANIFEST.in or package-data).

Found by a wheel/sdist divergence census of popular PyPI packages ([wheelproof](https://github.com/sethc555/wheelproof), results/divergence.md); self-check with `wheelproof divcheck --package `. Verified twice in clean python:3.12 containers with exact file-list agreement.