[KnifeLemon]

Why

`build (win-arm64)` hung at Build Explorer menu extension twice today (#1090 and #1101) until the two-hour job limit. The same step normally takes about two minutes there. The log stops right after `build FileeExplorerMenu.dll 2.3.0 (arm64)`, so it is `zig cc`, which runs under x64 emulation on the ARM runner.

What changes

• `build/build-explorer-menu.ps1` runs `zig cc` with an 8-minute limit per try and 3 tries. A try that runs over is stopped (with its child processes) and the next one uses a cache of its own. Compile errors still fail at once.
• In `ci.yml`, both Explorer menu steps get `timeout-minutes: 30`, so a hang can no longer take the whole job.

Tested

• x64 and arm64 builds locally: DLL and MSIX written as before.
• The retry loop on its own with a process that sleeps past the limit: it stops it, tries 3 times, then fails with a clear message.

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