Use tokio::spawn_blocking whenever we perform blocking steps

[RolandSherwin]

We should be using tokio::spawn_blocking instead of tokio::spawn whenever we are doing sync long running processing inside a task. As this might block the current tokio's worker thread, and will not allow other tasks to progress.

spawn_blocking will use its own thread pool with individual system thread for each task. https://docs.rs/tokio/latest/tokio/task/fn.spawn_blocking.html

We can also use tokio::fs whenever we are doing fs operations? This would automatically upgrade the task to run in its own thread.