Contribute `StableMemory`/`icfs` back to `cdk-rs`

[paulyoung]

The core crate here is necessary different to what is found in dfinity/cdk-rs.

The main differences are that there’s a single struct that implements the Read and Write traits, and the Seek trait is also provided.

If there isn’t a significant downside to doing that in the Rust SDK the goal should be to move it (and the tests) back upstream if it would be accepted.

Duplicating efforts here, in cdk-rs, and in other places like https://github.com/spinner-cash/lib-rs/blob/4ba800569bd45dccb3712ba232d5338a2fb8275c/src/storage.rs seems unnecessary.

[paulyoung]

@hpeebles what do you think about this?

[ncpenke]

@paulyoung In case you're interested I have an alternate approach here that layers the functionality on top of the existing cdk-rs API.

I also opened these tickets to potentially merge this work:
dfinity/cdk-rs#333
dfinity/cdk-rs#334

[paulyoung]

@ncpenke thanks for letting me know.

I spent a lot of time testing and fixing edge cases in my implementation so I’d be looking for the same test coverage in an alternative before I’d consider switching.

The examples in this repo double up as test suites. The low-level tests can be found here: https://github.com/codebase-labs/icfs/blob/8371ab72995ea4cd0d786de606a1e6b97a41be0a/examples/icfs/lib.rs

[ncpenke]

Thanks for the pointer @paulyoung. I'll run those tests and let you know the results.