Flaky test: RocksDB stable root closing times out after 2s

## Summary The RocksDB stable root test intermittently times out with a 2-second deadline when closing and reloading as converting. ## Failure Details **File**: RocksDB-related test (stable root operations) **Test**: `closing stable root, reload as converting` **Error**: `Alcotest__Core.Check_error("Error closing stable root, reload as converting timed out after 2s.")` **Observed in**: Nightly build [#1268](https://buildkite.com/o-1-labs-2/mina-mainline-branches-nightlies/builds/1268) on branch `dkijania/force-coverage-on-nightly` ## Log excerpt ``` Root 0 closing stable root, reload as converting.[FAIL] -- Root.000 [closing stable root, reload as converting.] Failed -- [exception] (monitor.ml.Error ("Alcotest__Core.Check_error(\"Error closing stable root, reload as converting timed out after 2s.\")")) 1 error! in 6.000s. 4 tests run. ``` ## Impact - Pre-existing flaky test unrelated to recent changes - 2s timeout may be too aggressive for CI environments under load (especially during `--force` full recompilation builds where I/O is heavier) ## Suggested Fix - Increase the timeout for this specific test (e.g., 10s or 30s) - Investigate whether disk I/O contention during parallel test execution contributes to the timeout