Fix intermittent installer hang on Windows

[twangboy]

What does this PR do?

Fix intermittent silent-mode installer hang on Windows; add NSIS test infrastructure

Upstream 3006.x worked around a known silent-mode installer hang with a wmic process kill — deprecated on Windows 11 and unreliable. This change fixes the root causes and replaces the workaround.

Salt-Minion-Setup.nsi:

• Replace wmic kill in .onInstSuccess and un.onUninstSuccess with System::Call "kernel32::ExitProcess(i 0)" guarded by ${If} ${Silent}. ExitProcess bypasses the NSIS message loop entirely, avoiding the cross-thread deadlock between the exec thread and UI thread that caused the hang.
• Replace nsExec::ExecToStack for service start with SimpleSC::StartService "salt-minion" "" 30. SimpleSC calls the SCM API inside the plugin DLL with no child process, pipe, or handle inheritance — eliminating the deadlock source.
• Replace nsExec::ExecToStack for stop/remove in un.uninstallSalt with SimpleSC::StopService (wait_for_file_release=1, timeout=30) and SimpleSC::RemoveService. Remove the 6-second sleep and three-pass PowerShell kill loop that were compensating for the old approach.
• Switch all nsExec::ExecToStack ssm.exe set calls in -Post and .onInstSuccess to nsExec::Exec (fire-and-forget); configuration commands need no stdout capture.
• Add taskkill belt-and-suspenders after SimpleSC stop/remove.
• Guard SetAutoClose true in uninstallSalt with !ifdef UNINSTALL so it does not fire during the upgrade path (.onInit calling uninstallSalt).
• Add SetAutoClose true in .onInit for silent mode and un.onInit.
• Push/Pop $R0 around Call uninstallSalt in .onInit: GetParent inside the function writes to $R0, clobbering the saved silent flag used to conditionally restore SetSilent normal afterward.
• Fix typo "mnually" and add missing Quit after VCRedist error.
• Remove InstallDirRegKey (unused).

conftest.py:

• Replace subprocess.PIPE with subprocess.DEVNULL. NSIS Exec passes inherited pipe handles to child processes (nssm, salt-minion), which hold the write-end open indefinitely; proc.communicate() never sees EOF, causing the test to block forever.
• Replace proc.communicate() with proc.wait() for the same reason.
• Reduce run_command timeout from 300 to 60 seconds.
• Add _kill_process_tree() to terminate the entire process hierarchy on timeout (not just the top-level installer process).
• Return True/False from run_command and assert in install_salt so a force-kill fails the test — detecting hangs is the purpose of this suite.
• Add _wait_for_processes() with SCM registry polling: waits for all PROCESSES to exit, INSTDIR to be deleted, and the salt-minion SCM key to disappear before the next iteration. Prevents ERROR_SERVICE_MARKED_FOR_DELETE races between iterations.
• Fix duplicate Un_D.exe entry in PROCESSES (should be Un_E.exe).

Test stubs (new files):

• stubs/daemon/: Go program that blocks on SIGINT, used as a realistic salt-minion.exe stub that NSSM can manage as a service.
• stubs/exit/: Go program that exits immediately with code 0, used as vcredist stub so ExecWait in the installer succeeds.

setup.ps1 / quick_setup.ps1:

• Build stubs with go build -C so Go module resolution finds go.mod regardless of the caller's working directory.
• Replace fake Set-Content vcredist binaries with real go build output.
• Add Go 1.20+ prerequisite check: look in PATH, then fall back to C:\Program Files\Go and C:\Go; download and install silently from salt-windows-deps if missing.

install_nsis.ps1:

• Update NSIS download URL from 3.10 to 3.11.
• Add SimpleSC plugin install section (ANSI + Unicode DLLs from nsis-plugin-simplesc.zip and nsis-plugin-simplescu.zip).

test.ps1:

• Capture $LASTEXITCODE immediately after pytest and exit with it after the completion banner, so CI/CD correctly fails the job when pytest reports failures or errors.
• Here are the logs from 3006.x Nightly (https://github.com/saltstack/salt/actions/runs/23825393770)
  NSIS Config Tests Log.txt
  NSIS Stress Tests Log.txt

Previous Behavior

NSIS Tests were failing, but not reporting failure.
Installer would hang intermittently.

New Behavior

Test failiures now bubble up.
Installer doesn't hang.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

Yes