flake.nix: Fix Python environment for nix build

The build was failing because Python packages in nativeBuildInputs
weren't available to the Python interpreter that CMake uses. This
happened due to nixpkgs changes in how Python packages work.

Changes:
- Create bundled Python environment using python.withPackages
- Add Python dependencies to zmake package so its sys.executable
  has access to required modules (pyyaml, pykwalify, etc.)
- Patch zmake to use bundled Python for CMake's Python3_EXECUTABLE
- Use --static flag to skip git version detection (sources don't
  have .git directories in nix build)
- Explicitly set ZEPHYR_SDK_INSTALL_DIR and force zephyr toolchain
- Update devShell to use bundled Python

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

Author: JohnAZoidberg

flake.nix

@@ -34,6 +34,16 @@
       python = pkgs.python312;
       pythonPkgs = pkgs.python312Packages;
 
+      # Bundled Python with all required packages for the build
+      buildPython = python.withPackages (ps: [
+        ps.pyyaml
+        ps.pykwalify
+        ps.packaging
+        ps.pyelftools
+        ps.colorama
+        ps.setuptools
+      ]);
+
       setProjectDynamicToLicense = ''
         ${pkgs.toml-cli}/bin/toml set pyproject.toml project.dynamic license | ${pkgs.moreutils}/bin/sponge pyproject.toml
         sed -e 's/dynamic = "license"/dynamic = ["license"]/' -i pyproject.toml
@@ -84,18 +94,17 @@
             pkgs.cmake
             pkgs.git
             pkgs.ninja
-            pythonPkgs.pyyaml
-            pythonPkgs.pykwalify
-            pythonPkgs.packaging
-            pythonPkgs.pyelftools
-            pythonPkgs.colorama
+            buildPython
             packages.binman
           ];
 
           dontUseCmakeConfigure = true;
 
+          # Ensure the zephyr SDK is found by zmake toolchain probing
+          ZEPHYR_SDK_INSTALL_DIR = "${zephyr-sdk}";
+
           buildPhase = ''
-            ${packages.zmake}/bin/zmake -j8 build ${build}
+            ${packages.zmake}/bin/zmake -j8 build --static -t zephyr ${build}
           '';
 
           installPhase = ''
@@ -121,12 +130,25 @@
         pyproject = true;
         build-system = [pythonPkgs.setuptools];
 
+        # These dependencies are needed by zmake's Python (sys.executable)
+        # which gets passed to CMake as Python3_EXECUTABLE
+        dependencies = [
+          pythonPkgs.pyyaml
+          pythonPkgs.pykwalify
+          pythonPkgs.packaging
+          pythonPkgs.pyelftools
+          pythonPkgs.colorama
+        ];
+
         postPatch = ''
           sed -e 's#"/bin:/usr/bin"#"/bin:/usr/bin:${pkgs.gcc}/bin:${pkgs.dtc}/bin:${pkgs.ninja}/bin"${
             if pkgs.stdenv.hostPlatform.isDarwin
             then '',"DYLD_LIBRARY_PATH":"${pkgs.dtc}/lib"''
             else ""
           }#' -i zmake/jobserver.py
+
+          # Replace sys.executable with the bundled Python that has all required packages
+          sed -e 's#"Python3_EXECUTABLE": sys.executable#"Python3_EXECUTABLE": "${buildPython}/bin/python3"#' -i zmake/zmake.py
         '';
       };
 
@@ -206,12 +228,7 @@
           pkgs.cmake
           pkgs.git
           pkgs.ninja
-          pythonPkgs.pyyaml
-          pythonPkgs.pykwalify
-          pythonPkgs.packaging
-          pythonPkgs.pyelftools
-          pythonPkgs.colorama
-          pythonPkgs.setuptools
+          buildPython
           packages.zmake
           packages.binman
         ];