Add 7z_x64 package for VirtIO-FS support_win_fs coverage.

7z_x64/.gitignore

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+*
+!.gitignore
+!config.json
+!install.ps1

7z_x64/config.json

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+{
+    "download_url": "https://github.com/ip7z/7zip/releases/download/26.02/7z2602-x64.msi",
+    "file_name": "7z-x64.msi",
+    "install_cmd": "powershell",
+    "install_args": "-ExecutionPolicy Bypass -File @sw_path@\\install.ps1 -MsiPath @sw_path@\\@file_name@",
+    "install_dest": "client",
+    "install_time": {
+        "kit": "after",
+        "driver": "before"
+    }
+}

7z_x64/install.ps1

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+param(
+    [Parameter(Mandatory = $true)]
+    [String]$MsiPath
+)
+
+$ErrorActionPreference = 'Stop'
+
+if (-not (Test-Path -LiteralPath $MsiPath)) {
+    throw "7z MSI not found: $MsiPath"
+}
+
+# Keep a copy for support_win_fs (elevate installer from virtiofs share).
+$stageDir = 'C:\7-Zip'
+New-Item -ItemType Directory -Force -Path $stageDir | Out-Null
+Copy-Item -Force -LiteralPath $MsiPath -Destination (Join-Path $stageDir '7z-x64.msi')
+
+$log = Join-Path $env:TEMP '7z-install.log'
+$p = Start-Process -FilePath 'msiexec.exe' -Wait -PassThru -ArgumentList @(
+    '/i', $MsiPath,
+    '/l*v', $log,
+    '/qn',
+    '/norestart'
+)
+
+if ($p.ExitCode -ne 0 -and $p.ExitCode -ne 3010) {
+    throw "msiexec 7z failed: exit $($p.ExitCode) (log=$log)"
+}
+
+$sevenZipExe = 'C:\Program Files\7-Zip\7z.exe'
+if (-not (Test-Path -LiteralPath $sevenZipExe)) {
+    throw "7z.exe missing after MSI install (expected $sevenZipExe, log=$log)"
+}
+
+Write-Output "PASS: 7z installed at $sevenZipExe; MSI staged at $stageDir\7z-x64.msi (msiexec exit $($p.ExitCode))"