fix: expose AsyncIPCProvider on AsyncWeb3

[suyua9]

Summary

• expose AsyncIPCProvider on AsyncWeb3, matching the other async provider convenience attributes
• add a small regression test for the class-level provider export

Rationale

AsyncIPCProvider is already exported from the package root, and the docs include examples that use AsyncWeb3.AsyncIPCProvider(...). Unlike AsyncHTTPProvider, WebSocketProvider, and AsyncEthereumTesterProvider, the AsyncWeb3 class did not expose this provider attribute, so those examples would fail at the symbol lookup step.

Testing

• .venv/bin/python -m pytest tests/core/providers/test_provider_init.py -q -k 'async_web3_exposes_async_ipc_provider'
• python3 -m py_compile web3/main.py tests/core/providers/test_provider_init.py
• git diff --check

Note: running the full tests/core/providers/test_provider_init.py file in this local lightweight venv failed only for the existing EthereumTester provider parametrizations because eth_tester was not installed. The new focused regression test passed.