Replace the usage of HTTPX with Impit

[vdusek]

We still use httpx here, e.g.:

• apify-sdk-python/src/apify/log.py

  Line 30 in df380d2

  # Silence HTTPX logger unless debug logging is requested

• apify-sdk-python/src/apify/scrapy/_logging_config.py

  Line 40 in df380d2

  # Set the 'httpx' logger to a less verbose level.

• apify-sdk-python/pyproject.toml

  Line 42 in df380d2

  "httpx>=0.27.0",

• apify-sdk-python/src/apify/_proxy_configuration.py

  Line 10 in df380d2

  import httpx

• apify-sdk-python/tests/unit/conftest.py

  Line 196 in df380d2

  def patched_httpx_client(monkeypatch: pytest.MonkeyPatch) -> Iterator[None]: