chore(release): v1.9.0

[makegov-mark]

Release v1.9.0.

Minor rather than patch: this ships the GSA eBuy requests resource (four methods, the EbuyAccess result type, the EbuyRequest / EbuyAttachment schemas), the new TangoAttachmentLinkError, and ebuy_request as an alert query type (#70). All additive; no existing call changes meaning.

• pyproject.toml, tango/__init__.py and uv.lock bumped together.
• [Unreleased] graduated to ## [1.9.0] - 2026-09-28.

Verified

• uv build produces tango_python-1.9.0.tar.gz and tango_python-1.9.0-py3-none-any.whl.
• tango.__version__ reads 1.9.0.
• uv lock --check passes.
• uv run ruff format --check tango/, uv run ruff check tango/ and uv run mypy tango/ pass (the same scope as lint.yml).
• uv run pytest tests/ -m "not integration": 449 passed, 30 skipped.

Merging this does not publish

publish.yml triggers on release: [published] (or a manual dispatch), not on a push to main. Creating the v1.9.0 GitHub Release after merge is what ships to PyPI, and PyPI versions are immutable once uploaded.

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