Add Copilot setup workflow for R development environment (#159)

* Initial plan

* Add copilot-setup-steps.yml workflow for R development environment

Co-authored-by: ms609 <1695515+ms609@users.noreply.github.com>

* Fix action versions to match existing workflows (use checkout@v4)

Co-authored-by: ms609 <1695515+ms609@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ms609 <1695515+ms609@users.noreply.github.com>

Author: Copilot

.github/workflows/copilot-setup-steps.yml

@@ -0,0 +1,61 @@
+name: "Copilot Setup Steps"
+
+# Automatically run the setup steps when they are changed to allow for easy validation, and
+# allow manual testing through the repository's "Actions" tab
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    # Set the permissions to the lowest permissions possible needed for your steps.
+    # Copilot will be given its own token for its operations.
+    permissions:
+      # Need contents: read to clone the repository and TreeTools for debugging support
+      contents: read
+
+    # You can define any steps you want, and they will run before the agent starts.
+    # If you do not check out your code, Copilot will do this for you.
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up R
+        uses: r-lib/actions/setup-r@v2
+        with:
+          r-version: 'release'
+          # Include custom repository for TreeTools and TreeDistData packages
+          extra-repositories: https://ms609.github.io/packages/
+
+      - name: Install system dependencies (Linux)
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y texlive-latex-base libglpk-dev texlive-fonts-recommended
+
+      - name: Set up R dependencies
+        uses: r-lib/actions/setup-r-dependencies@v2
+        with:
+          extra-packages: |
+            ms609/TreeDistData
+            devtools
+            testthat
+            roxygen2
+            lintr
+          needs: |
+            check
+
+      - name: Checkout TreeTools source (for debugging support)
+        uses: actions/checkout@v4
+        with:
+          repository: ms609/TreeTools
+          path: TreeTools-source
+          # This provides access to TreeTools source code for agents to inspect
+          # when debugging issues in TreeDist that may relate to TreeTools