Fix: Run scons via venv Python to find packaging module

The issue was that packaging was installed in the venv, but scons was
being run with the system Python, which couldn't see the venv's packages.

Solution:
1. Install scons in the venv (along with other dependencies)
2. Run scons using: venv/bin/python -m SCons

This ensures scons runs with the venv's Python environment and can
import the packaging module and other dependencies we installed.

Author: sbryngelson

packaging/homebrew/mfc.rb

@@ -36,11 +36,12 @@ def install
 
     # Build and install Cantera 3.1.0 from source BEFORE MFC build
     resource("cantera").stage do
-      # Install Cantera build dependencies
-      system venv/"bin/pip", "install", "cython", "numpy", "ruamel.yaml", "packaging"
+      # Install Cantera build dependencies (including scons)
+      system venv/"bin/pip", "install", "cython", "numpy", "ruamel.yaml", "packaging", "scons"
 
       # Configure Cantera build
-      system "scons", "build",
+      # Run scons with the venv's Python so it can find installed packages
+      system venv/"bin/python", "-m", "SCons", "build",
              "python_package=y",
              "f90_interface=n",
              "system_sundials=y",
@@ -53,7 +54,7 @@ def install
              "-j#{ENV.make_jobs}"
 
       # Install Cantera
-      system "scons", "install"
+      system venv/"bin/python", "-m", "SCons", "install"
 
       # Install Cantera Python package into venv
       cd "build/python" do