test(windows): backport server test repairs from #4862

Reduce the SQLite concurrency fixture to five iterations per writer on
Windows so slow fsync does not exhaust the busy timeout. Hold mutation
stress-test locks until a wall-clock deadline rather than depending on
Windows timer granularity.

Retain Windows' existing portable supervisor fixtures. The isolation
validation modules changed by #4862 are not present on this branch.

Native Windows ARM64 validation: 6630 tests passed, 41 skipped, 0 failed.

Backported from commit 92434dcb2b.

Signed-off-by: Shailendra Singh <shailendras@nvidia.com>

crates/openshell-server/src/compute/mutation_guard.rs

@@ -1164,7 +1164,11 @@ mod tests {
         if op.is_distributed() {
             fleet.enter(op);
         }
-        tokio::time::sleep(hold).await;
+        // Windows timers round a 1 ms sleep up to ~16 ms, so yield instead.
+        let until = std::time::Instant::now() + hold;
+        while std::time::Instant::now() < until {
+            tokio::task::yield_now().await;
+        }
         if op.is_distributed() {
             fleet.leave(op);
         }

crates/openshell-server/src/persistence/tests.rs

@@ -2298,7 +2298,8 @@ async fn sqlite_concurrent_writes_return_their_own_resource_version() {
     use std::sync::Arc;
 
     const WRITERS: u64 = 8;
-    const WRITES: u64 = 25;
+    // Slow Windows fsync can starve a writer past the SQLite busy timeout.
+    const WRITES: u64 = if cfg!(windows) { 5 } else { 25 };
 
     let tmp = tempfile::tempdir().expect("tempdir");
     let url = on_disk_store_url(&tmp.path().join("openshell.db"));