Wrap blocking APIs with tokio

Some subcommands such as `chrs login` call blocking APIs (wait for keyboard input). This blocks the async runtime, which is fine in this context, but a bad practice.

https://docs.rs/tokio/1.15.0/tokio/task/index.html#blocking-and-yielding

Start by tracing the subcommands, especially `chrs login`, that wait for keyboard input, then read Tokio's blocking-and-yielding documentation linked in the issue. Done means the identified blocking APIs no longer block the async runtime while preserving the existing command behavior.

Written by the indexing model from the issue text.