• Upgrade Rust edition and rustc version to bring in some nice features, e.g. let chains instead of nested if block.
• Fix clippy and format due to the upgrade.
• Fix a bug identified by the new rustc:

  xet-core/xet_runtime/src/runtime.rs

  Line 195 in 6cb0a7f

  TokioRuntimeBuilder::new_multi_thread().worker_threads(get_num_tokio_worker_threads())

#[cfg(not(target_family = "wasm"))]
{
    // A new multithreaded runtime with a capped number of threads
    TokioRuntimeBuilder::new_multi_thread().worker_threads(get_num_tokio_worker_threads())
}

here the end curly bracket drops the temporary builder while a &mut Self to the dropped value is returned. (this may be due to a difference between compilers regarding how they treat the scope of "{...}" of #[cfg(...))] {...}?)