chore: add snippets for dev docs, corrected some docstring examples in cache client

[anitarua]

Addresses #210

[anitarua]

examples are currently using the local SDK, but once we cut a release we can update this here and probably find a way to verify examples in CI

[malandis]

Thanks for doing this. As a discussion point, I see two things:

1. In the examples should we use the ?-operator to propagate errors up from the client calls?
2. Should we test for particular error cases in some examples?

To illustrate, in some snippets we use the ?-operator on the cache calls, then display the answer in the happy case.

On others we match on the result and display an error.

On others we test for particular error codes, eg:

    match cache_client.set(cache_name, "key", "value").await {
        Ok(_) => println!("Set successful"),
        Err(e) => {
            if let MomentoErrorCode::NotFoundError = e.error_code {
                println!("Cache not found: {}", cache_name);
            } else {
                eprintln!("Error setting value in cache {}: {}", cache_name, e);
            }
        }
    }

My inclination given Rust's features is to:

1. Bubble up the errors using ?
2. Match on all the other cases (hit vs miss, stored vs not stored, cache created vs already exists)

We can socialize the options with the team during the bug bash.

[malandis]

Couple small issues. Looks great otherwise and much improved and cleaner.