## Why
Elevated Windows sandbox tests share machine-wide accounts. Running them in the sharded core suite can consume test deadlines while shards wait for the account lock.
## What changed
Move the Windows sandbox tests into the Windows-only `windows_sandbox` integration-test binary. Update the nextest account-sharing group to select the entire binary instead of individual test names, so tests queue before their timeouts start. Keep the existing guard for coordination with other test binaries.
GitOrigin-RevId: 613925c9398b5acc8440fa34c658680f31f65c8b
