Statement::Finalize blocks nodejs event loop

[alex3d]

Statement::Finalize runs entirely in main/event loop thread and could block event loop on sqlite3_finalize (if some other query currently executing in libuv thread pool). sqlite3_finalize should be called only from thread pool as any other sqlite3_ functions.

Wall clock profiling flamegraph:

I could make PR if there is no rationale to run sqlite3_finalize in event loop thread.

[daniellockyer]

@alex3d I'd love to see a PR 🙂