Add Boost dependency to CI workflow

The C++ backend requires Boost for r_c_shortest_paths algorithm.
Install libboost-dev (Ubuntu) and boost (macOS) in both test and
build-wheels jobs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: miladbarooni

.github/workflows/tests.yml

@@ -27,12 +27,12 @@ jobs:
       if: runner.os == 'Linux'
       run: |
         sudo apt-get update
-        sudo apt-get install -y cmake build-essential
+        sudo apt-get install -y cmake build-essential libboost-dev
 
     - name: Install system dependencies (macOS)
       if: runner.os == 'macOS'
       run: |
-        brew install cmake
+        brew install cmake boost
 
     - name: Cache pip packages
       uses: actions/cache@v4
@@ -115,10 +115,21 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
 
+    - name: Install system dependencies (Ubuntu)
+      if: runner.os == 'Linux'
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y cmake build-essential libboost-dev
+
+    - name: Install system dependencies (macOS)
+      if: runner.os == 'macOS'
+      run: |
+        brew install cmake boost
+
     - name: Install build dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install build wheel
+        pip install build wheel pybind11
 
     - name: Build wheel
       run: |