feat(windows): replace php-sdk-binary-tools with MSYS2 + 7za-win

- Add msys2-build-essentials target: downloads the MSYS2 nightly sfx,
  extracts it, disables PGP keyring (CI-safe), runs two-pass pacman
  update, and installs autotools build essentials (make, autoconf,
  automake, libtool, pkgconf, perl).
- Add 7za-win target: downloads 7za.exe to PKG_ROOT_PATH\bin.
- Remove php-sdk-binary-tools target and all PHP_SDK_PATH references;
  replace with SPC_MSYS2_PATH throughout Artifact, ArtifactExtractor,
  FileSystem, DefaultShell and MSVCToolchain.
- Replace {php_sdk_path} path placeholder with {spc_msys2_path}.
- WindowsToolCheck: replace checkSDK/installSDK with checkMsys2,
  installMsys2 and check7zaWin/install7zaWin fix items.
- nasm.yml: extract nasm.exe/ndisasm.exe to {pkg_root_path}/bin.
- env.ini: rename PHP_SDK_PATH to SPC_MSYS2_PATH.
- Docs: update Windows migration guide and package-model placeholder docs.

docs/zh/develop/package-model.md

@@ -223,7 +223,7 @@ openssl:
 | `{working_dir}` | 工作目录（项目根目录） |
 | `{download_path}` | 下载缓存目录（`downloads/`） |
 | `{source_path}` | 解压源码目录（`source/`） |
-| `{php_sdk_path}` | Windows PHP SDK 目录 |
+| `{spc_msys2_path}` | MSYS2 根目录（`msys64/`）——仅 Windows |
 
 ## target 包类型