fix: replace depricated async-std with smol

[sauhardh]

This PR implements the smol runtime replacing the async-std because it's depricated

Some changes:

• Replaced async-std with smol and included alias name spawn_blocking for smol::unblock.
• replacing closure with function itself io::Error::other(e).

Test Pass:

• [☑️] cargo test
• [☑️] cargo test -p http-cache-stream-reqwest
• [☑️] cargo clippy --all
• [☑️] cargo +nightly fmt --check
• [☑️] cargo doc

Related Issue:
#8

[peterhuene]

Hi @sauhardh.

Thanks very much for implementing this!

Looks great, just two tiny nits in the formatting of Cargo.toml entries, but otherwise ready to go!

[peterhuene]

One thing that is missing is an update to .github/workflows/CI.yml to pass the new feature flag instead of async-std.

[sauhardh]

@peterhuene Thankyou for guidance, I have again updated the code based on your review. Please review and let me know if something need to be changed.

[peterhuene]

Hi @sauhardh. Thanks very much for the contribution!

I'll merge once CI goes green.