feat: exchange rate example in Rust

[ielashi]

Adds an example of how to fetch an exchange rate from the exchange rate canister. This example is intended to be showcased on ICP Ninja along with a tutorial in https://internetcomputer.org/docs/defi/

[ielashi]

Looks like tokenmania is failing CI. It's unclear to me why given that this PR doesn't touch it in any form.

[marc0olo]

Looks like tokenmania is failing CI. It's unclear to me why given that this PR doesn't touch it in any form.

@ielashi I assume it was a change in the icrc_ledger_types crate which might have been updated.

the example defines icrc-ledger-types = "0.1.6", the log prints Downloaded icrc-ledger-types v0.1.12

[ielashi]

Looks like tokenmania is failing CI. It's unclear to me why given that this PR doesn't touch it in any form.

@ielashi I assume it was a change in the icrc_ledger_types crate which might have been updated.

the example defines icrc-ledger-types = "0.1.6", the log prints Downloaded icrc-ledger-types v0.1.12

This is independent of this change - I think master is broken. I'll fix it in a separate PR. In the meantime, please have a look at this project.

[marc0olo]

@ielashi is it intentional that you didn't add a README? 🤔

I just recognized that this is also the case in the receiving-icp example.

this might also lead to some weird behavior on ICP Ninja. I just remember that I recently checked this with @raymondk and this is what Ninja shows in the UI for receiving-icp (cc @fxgst @viviveevee) :