feat: add type stubs for miniupnpc

[GautamBytes]

What was wrong?
The type checker (pyrefly) failed when importing miniupnpc because it is a C extension without native type stubs. A previous quick-fix (PR #1010) used a # type: ignore comment to bypass the error, but this did not provide proper type safety or IDE support for developers.

Issue #1009

How was it fixed?
Following the long-term solution suggested in the issue, I implemented the following changes:

• Created Type Stubs: Added stubs/miniupnpc/init.pyi with type annotations for the specific methods used by libp2p (discover, selectigd, externalipaddress, addportmapping, and deleteportmapping).
• Updated Tooling Configuration: Modified pyproject.toml to include the new stubs directory in the pyrefly search path.
• Code Cleanup: Removed the now-unnecessary # type: ignore[import-untyped] comment from libp2p/discovery/upnp/upnp.py.
• Verified Types and Logic: Confirmed that pyrefly now passes with 0 errors on the affected module and that all 10 UPnP-related unit tests pass successfully.

(venv) gautammanch@Gautams-MacBook-Air py-libp2p % pyrefly check libp2p/discovery/upnp/upnp.py
 INFO 0 errors shown, 0 errors ignored, 1 modules, 94 transitive dependencies, 25,956 lines, took 0.36s (checking 0.05s), peak memory physical 95.9 MiB
(venv) gautammanch@Gautams-MacBook-Air py-libp2p % pytest tests/core/discovery/upnp/test_upnp.py
================================================================================= test session starts =================================================================================
platform darwin -- Python 3.12.12, pytest-9.0.2, pluggy-1.6.0 -- /Users/gautammanch/py-libp2p/venv/bin/python3.12
cachedir: .pytest_cache
rootdir: /Users/gautammanch/py-libp2p
configfile: pyproject.toml
plugins: mock-3.15.1, anyio-1.4.0, xdist-3.8.0, timeout-2.4.0, trio-0.8.0, Faker-40.1.2, rerunfailures-16.1
collected 10 items                                                                                                                                                                    

tests/core/discovery/upnp/test_upnp.py::test_upnp_discover_success PASSED                                                                                                       [ 10%]
tests/core/discovery/upnp/test_upnp.py::test_upnp_discover_with_success_exception PASSED                                                                                        [ 20%]
tests/core/discovery/upnp/test_upnp.py::test_upnp_discover_no_devices_found PASSED                                                                                              [ 30%]
tests/core/discovery/upnp/test_upnp.py::test_upnp_discover_double_nat PASSED                                                                                                    [ 40%]
tests/core/discovery/upnp/test_upnp.py::test_add_port_mapping_success PASSED                                                                                                    [ 50%]
tests/core/discovery/upnp/test_upnp.py::test_add_port_mapping_failure_no_discover PASSED                                                                                        [ 60%]
tests/core/discovery/upnp/test_upnp.py::test_add_port_mapping_exception PASSED                                                                                                  [ 70%]
tests/core/discovery/upnp/test_upnp.py::test_remove_port_mapping_success PASSED                                                                                                 [ 80%]
tests/core/discovery/upnp/test_upnp.py::test_upnp_discover_invalid_igd PASSED                                                                                                   [ 90%]
tests/core/discovery/upnp/test_upnp.py::test_upnp_discover_selectigd_failure PASSED                                                                                             [100%]

================================================================================ slowest 50 durations =================================================================================
1.77s setup    tests/core/discovery/upnp/test_upnp.py::test_upnp_discover_success

(29 durations < 0.005s hidden.  Use -vv to show these durations.)
================================================================================= 10 passed in 1.81s ==================================================================================

To-Do
[x] Clean up commit history
[x] Add or update documentation related to these changes
[x] Add entry to the release notes