Honor --no-header in distributed terminal reporting

[SAY-5]

Running pytest with --no-header -n1 still prints worker startup/status lines and, with -v, the scheduling banner. Respect --no-header in the xdist header paths while keeping worker error messages, test results and scheduling intact.

Fixes #958, following the scope suggested in #958 (comment). This does not add serial-style collected/deselected counts.

Tests cover TTY and non-TTY reporting, different-interpreter banners, normal header output, worker errors, and one-worker runs at default/quiet/verbose levels with passing, skipped and failing tests. Before the change, five regression cases fail and five controls pass; all ten pass afterward.

Validation on macOS ARM64 with CPython 3.13.9, pytest 8.4.2 and execnet 2.1.2:

• Complete test_dsession.py, test_plugin.py and TestTerminalReporting: 82 passed, one optional-psutil skip and two existing expected failures.
• Pinned Ruff 0.16.5 lint and formatting checks passed for all 32 Python files.

The full suite, other interpreter/platform combinations and remaining pre-commit hooks were not run locally.

AI assistance: Codex assisted with the implementation, regression tests, review and this description.

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[RonnyPfannschmidt]

🤖 Written by Claude Opus 5.5 via Claude Code for the pytest-xdist maintainers; I prompted it, it did the work, I read it.

LGTM, this matches the scope suggested in #958. I checked it locally with -n2 --no-header. With and without -v, the worker status lines (created:, the per-worker Python/cwd lines, N workers [M items], scheduling tests via ...) are all gone. Test results and node down: errors still show.

One thing we might want to nitpick, now or as a follow-up: N workers [M items] is also xdist's only equivalent of collected N items. Plain pytest keeps that line under --no-header:

$ pytest --no-header
collected 2 items
$ pytest --no-header -n2
(no count at all with this PR)

So -n runs now print less than serial runs. We could keep printing the item count (for example as collected M items once collection is done), or accept dropping it as #958 suggested. I'm fine with either, but we should decide on purpose.

The py311-pytestmain failures are in TestGroupScope, which this PR doesn't touch. I think they come from changes in pytest main.

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