Gas management

[kostekIV]

I ve been tryin the Sui Rust SDK and noticed that coin management for transactions is more cumbersome compared to the TypeScript SDK. I htink it applies to this repository and also to https://github.com/MystenLabs/sui/blob/main/crates/sui-sdk/Cargo.toml that management of the coins for tx is a little bit rough.

1. we need to provide gas-payment ourselves (fetching from network checking if the balance is ok etc).
2. In scenario when we want to send multiple txs concurrently we also need to manage which coins are used/locked, versions et.

My proposition is to add 2 things:

1. automatic gas-payement objects fetching - like it is in typescript sdk
2. Something similar to parallel executor, again from ts sdk

I'm happy to help implement these features if you think they'd be good additions to the SDK.

[kostekIV]

Hey @bmwill,

I had some free time and went ahead with a proof of concept to showcase what I had in mind. You can find it here: https://github.com/kostekIV/sui-gas-provider.

If you have time, let me know your thoughts :)