macOS: centralise Python build dependencies using uv

[tallpsmith]

Problem

Python build dependencies for macOS PCP are defined in at least four places with no single source of truth:

Location	Purpose	pip3 deps
.github/workflows/macOS.yml	CI build	lxml openpyxl OrderedDict psycopg2-binary prometheus_client pyarrow pyodbc requests
.cirrus.yml	Tart VM build	none
qa/admin/package-lists/Darwin+*	QA test deps	requests setuptools openpyxl libvirt-python Pillow-PIL prometheus_client elasticsearch psycopg2
Developer's machine	local build	whatever they remembered

Additionally, Homebrew Python 3.14+ returns externally-managed-environment on bare pip3 install, making system-level installs impossible. The GitHub Actions CI already works around this with a manual venv (python3 -m venv pybuilddeps), but the Cirrus/Tart build and local development don't.

The CI also hardcodes PYTHONPATH="/usr/local/lib/python3.13/site-packages" (line 256 of macOS.yml) and pins Python 3.13 via actions/setup-python — both fragile assumptions that will break on version bumps.

Proposed Solution

Mandate uv (brew install uv) as the Python package manager for macOS builds. No pip fallback — one tool, one path.

New files

build/mac/requirements-build.txt — Python packages that affect what ./configure probes for:

requests
setuptools

build/mac/requirements-test.txt — additional packages for QA/testing:

-r requirements-build.txt
lxml
openpyxl
prometheus_client
psycopg2-binary

build/mac/setup-python-env.sh — single script used by both CI pipelines and developers:

#!/bin/bash
set -e
VENV_DIR="${1:-.pcp-venv}"
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
REQS="${2:-$SCRIPT_DIR/requirements-build.txt}"

uv venv "$VENV_DIR"
uv pip install --python "$VENV_DIR/bin/python3" -r "$REQS"

echo "Python build environment ready. Activate with:"
echo "  source $VENV_DIR/bin/activate"

CI updates

.github/workflows/macOS.yml:

• Remove actions/setup-python@v6 step (use Homebrew Python instead of pinning a version)
• Add uv to brew install step
• Replace inline pip install block with ./build/mac/setup-python-env.sh
• Remove hardcoded PYTHONPATH="/usr/local/lib/python3.13/site-packages" hack
• Remove hardcoded Python version references

.cirrus.yml:

• Add uv to brew install line in populate_script
• Add Python venv setup step before build
• Activate venv in pcp_build_script

Also update

• .gitignore — add .pcp-venv
• build/mac/CLAUDE.md — add uv to prerequisites
• build/mac/MACOS_DEVELOPMENT.md — developer setup instructions

Why uv?

• brew install uv — first-class Homebrew citizen
• 10-100x faster than pip for installs
• Handles venv creation natively (uv venv)
• Standalone Rust binary — no Python package needed

Verification

• ./configure output shows PMDA_OPENMETRICS ... yes and PMDA_OPENTELEMETRY ... yes
• python3 -c 'import requests' succeeds inside the venv
• Both CI pipelines build successfully
• No hardcoded Python version strings remain in CI files