CI failures on macOS/Windows:
1. `test_endpoint_rejects_null_byte` — ``monkeypatch.setenv("HF_ENDPOINT",
"...\x00")`` raises ``ValueError: embedded null byte`` at the C-level
setenv call on macOS/Windows before ``resolve_endpoint`` can reject it.
Linux's setenv swallows it. Replace with ``monkeypatch.setattr`` on
``os.environ`` dict so the null-byte string reaches ``resolve_endpoint``
on every platform.
2. Help-text substring tests (``test_train_shows_push_as_flag_in_help``,
``test_push_shows_collection_flag_in_help``, ``test_push_subcommand_exists``,
``test_hf_space_help_shows_flags``, ``test_train_help_shows_hf_resume``,
``test_hf_space_command_registered``) — Typer injects ANSI escape codes
on macOS/Windows pytest runs, splitting tokens like ``--push-as`` into
``-`` + ``-push-as`` across escape groups. Add ``_plain()`` helper that
strips ANSI via regex and use it in every help-text assertion.
Same pattern as 899ad8e (test_eval_gate.py) did after the v0.26.0 CI
Windows failure.
Full suite still passes locally: 100 HF integration tests in 3.25s.
Alpamys