feat(tool): bundle python for the meson build

- add a python-win tool package that unzips the official python.org
  nuget package into the pkgroot (venv and ensurepip included)
- meson uses it to build its venv and only falls back to a system
  python, so no manual environment setup is needed

config/pkg/lib/postgresql.yml

@@ -18,6 +18,7 @@ postgresql:
     - openssl
     - zlib
   tools@windows:
+    - python-win
     - meson
     - ninja
     - winflexbison

config/pkg/tool/python-win.yml

@@ -0,0 +1,8 @@
+python-win:
+  type: tool
+  artifact:
+    binary: custom
+  tool:
+    provides:
+      - python.exe
+    binary-subdir: python-win/tools

src/Package/Artifact/meson_win.php

@@ -22,8 +22,11 @@ class meson_win
         $dir = dirname($target_path);
         $venv = "{$dir}\\venv";
 
+        // Prefer the python-win tool package (installed alongside via tools@windows),
+        // fall back to whatever Python the machine already has.
+        $candidates = ['"' . PKG_ROOT_PATH . '\python-win\tools\python.exe"', 'python', 'py -3'];
         $python = null;
-        foreach (['python', 'py -3'] as $candidate) {
+        foreach ($candidates as $candidate) {
             [$code] = cmd()->execWithResult("{$candidate} --version", false);
             if ($code === 0) {
                 $python = $candidate;
@@ -31,7 +34,7 @@ class meson_win
             }
         }
         if ($python === null) {
-            throw new EnvironmentException('meson needs Python 3 on PATH. Install it from https://www.python.org or with `winget install Python.Python.3.13`.');
+            throw new EnvironmentException('meson needs Python 3; the python-win tool package did not install and no system Python was found.');
         }
 
         if (is_dir($venv)) {

src/Package/Artifact/python_win.php

@@ -0,0 +1,66 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Package\Artifact;
+
+use StaticPHP\Artifact\ArtifactDownloader;
+use StaticPHP\Artifact\Downloader\DownloadResult;
+use StaticPHP\Artifact\Downloader\Type\CheckUpdateResult;
+use StaticPHP\Attribute\Artifact\AfterBinaryExtract;
+use StaticPHP\Attribute\Artifact\CustomBinary;
+use StaticPHP\Attribute\Artifact\CustomBinaryCheckUpdate;
+use StaticPHP\Exception\DownloaderException;
+
+/**
+ * Full CPython for Windows from the official python.org nuget package. It is a plain zip
+ * (python.exe plus stdlib under tools/, venv and ensurepip included), so it installs into
+ * the pkgroot without touching the system. Used by the meson tool package.
+ */
+class python_win
+{
+    #[CustomBinary('python-win', [
+        'windows-x86_64',
+    ])]
+    public function downBinary(ArtifactDownloader $downloader): DownloadResult
+    {
+        $version = $this->getLatestVersion($downloader->getRetry());
+
+        $url = "https://api.nuget.org/v3-flatcontainer/python/{$version}/python.{$version}.nupkg";
+        // .nupkg is a zip; name the cache file .zip so the extractor treats it as one
+        $path = DOWNLOAD_PATH . DIRECTORY_SEPARATOR . "python-win-{$version}.zip";
+        default_shell()->executeCurlDownload($url, $path, retries: $downloader->getRetry());
+
+        return DownloadResult::archive(basename($path), ['url' => $url, 'version' => $version], extract: '{pkg_root_path}/python-win', version: $version);
+    }
+
+    #[CustomBinaryCheckUpdate('python-win', ['windows-x86_64'])]
+    public function checkUpdateBinary(?string $old_version): CheckUpdateResult
+    {
+        $version = $this->getLatestVersion();
+        return new CheckUpdateResult(
+            old: $old_version,
+            new: $version,
+            needUpdate: $old_version === null || $version !== $old_version,
+        );
+    }
+
+    #[AfterBinaryExtract('python-win', ['windows-x86_64'])]
+    public function afterExtract(string $target_path): void
+    {
+        if (!file_exists("{$target_path}\\tools\\python.exe")) {
+            throw new DownloaderException("Python installation appears incomplete: python.exe not found at {$target_path}\\tools\\python.exe");
+        }
+    }
+
+    private function getLatestVersion(int $retries = 0): string
+    {
+        $index = default_shell()->executeCurl('https://api.nuget.org/v3-flatcontainer/python/index.json', retries: $retries);
+        $versions = $index ? (json_decode($index, true)['versions'] ?? []) : [];
+        $stable = array_filter($versions, fn ($v) => preg_match('/^\d+\.\d+\.\d+$/', $v));
+        if ($stable === []) {
+            throw new DownloaderException('Failed to get Python versions from the nuget index');
+        }
+        return end($stable);
+    }
+}