Remove support for IronPython 2.7

[gonzalocasas]

IronPython 2.7 has been unmaintained for years and Rhino 8 ships CPython, so the compatibility layer no longer buys anything.

Removed

• The ironpython CI workflow and tests/ipy_test_runner.py it drove.
• compas_rrc.__install — the plugin only served python -m compas_rhino.install for Rhino 6/7. compas_fab and compas_eve both dropped their equivalents; Rhino 8 installs with pip.
• The IronPython Grasshopper componentizer wiring in tasks.py and release.yml. It pointed at src/compas_rrc/ghpython/components, which does not exist in this repo, so it was dead config either way.
• Python 2 era idioms IronPython required: from __future__ imports, explicit object bases, two-argument super().
• [bdist_wheel] universal = 1, meaningless for a Python 3 only package.

Changed

• Python floor is now 3.9 (matching compas_fab), declared via python_requires.
• CI matrices move from 3.8–3.10 to 3.9–3.13.

Tests pass locally against compas_fab 1.1.4 / compas 2.15.1.

Part of a series of maintenance PRs. Standalone — no dependency on the others.

🤖 Generated with Claude Code

[gonzalocasas]

Evidence that IronPython support was already non-functional, rather than something this PR is dropping while it still worked:

The windows-ironpython job fails on #27 too, and #27 only touches .gitignore and CHANGELOG.md. The cause is environmental — IronPython 2.7's pip cannot install the current COMPAS sdists any more:

IOError: [Errno 2] Could not find file '...\pip-o6vxz0-build\setup.py'
Command "python setup.py egg_info" failed with error code 1

compas, compas_robots and compas_fab are all pyproject-only now, and IronPython's pip predates PEP 517, so it falls back to setup.py egg_info and finds nothing. The workflow has been red for whatever COMPAS release first dropped setup.py.