Map public challenge redirects to login required

[subzeroid]

Fixes #1093

Instagram can redirect public web GraphQL/user-info requests to /challenge/?next=... and return an HTML page with status 200. public_request(..., return_json=True) previously treated that as a generic JSON decode failure.

This maps challenge redirect HTML to ClientLoginRequired, matching the existing /login/ redirect handling and allowing existing public lookup retry/session-injection paths to run.

Verification:

• .venv/bin/python -m pytest -q tests/regression/test_public.py::PublicRegressionTestCase::test_public_request_maps_challenge_redirect_html_to_login_required
• .venv/bin/python -m pytest -q tests/regression/test_request_logging.py::RequestLoggingRegressionTestCase::test_public_json_decode_error_log_truncates_response_body
• .venv/bin/python -m pytest -q tests/regression
• .venv/bin/python -m ruff check .
• .venv/bin/python -m ruff format --check .
• .venv/bin/python -m bandit -c pyproject.toml -r instagrapi
• .venv/bin/python -m build