Add cross-platform PR CI workflow for master with R CMD check + animl_env Python setup

[Copilot]

This PR adds a GitHub Actions CI workflow for animl-r pull requests targeting master, with full package checks and test execution via rcmdcheck. It also provisions the required reticulate-accessible Python environment (animl_env) with animl-py installed.

• Trigger + execution matrix

  • New workflow: .github/workflows/R-CMD-check.yaml
  • Runs only on pull_request to master
  • Matrix across ubuntu-latest, macos-latest, and windows-latest
  • Uses R release

• Python/reticulate dependency bootstrap

  • Sets up Python 3.12
  • Creates virtualenv at ~/.virtualenvs/animl_env
  • Installs animl-py into that env
  • Exposes env to reticulate via:
    • WORKON_HOME=~/.virtualenvs
    • RETICULATE_PYTHON=<animl_env python>

• R package checks + failure artifacts

  • Installs R dependencies (including rcmdcheck)
  • Runs rcmdcheck::rcmdcheck(..., check_dir = "check")
  • Uploads check/ artifacts on failure for triage

• Workflow hardening

  • Adds explicit minimal token scope:
    • permissions: { contents: read }

on:
  pull_request:
    branches: [master]

permissions:
  contents: read

- uses: actions/setup-python@v5
  with:
    python-version: '3.12'

- name: Create animl_env and install animl-py
  run: |
    VENV_DIR="$HOME/.virtualenvs/animl_env"
    python -m venv "$VENV_DIR"
    "$VENV_DIR/bin/python" -m pip install --upgrade pip
    "$VENV_DIR/bin/python" -m pip install animl-py
    echo "WORKON_HOME=$HOME/.virtualenvs" >> "$GITHUB_ENV"
    echo "RETICULATE_PYTHON=$VENV_DIR/bin/python" >> "$GITHUB_ENV"