feat: add new rates controller for non-EVM chains (#4242)

As part of the non-EVM initiative, there's a need to develop a new controller capable of fetching the rates for these blockchains. Currently, we can't rely on the `CurrencyRatesController` since it's dependent on the activity of the `NetworkController`, which is exclusively EVM oriented.

Co-authored-by: gantunesr <gantunesr@users.noreply.github.com>
Co-authored-by: Elliot Winkler <elliot.winkler@gmail.com>
Co-authored-by: Charly Chevalier <charly.chevalier@consensys.net>

packages/assets-controllers/README.md

@@ -19,12 +19,41 @@ This package features the following controllers:
 - [**CollectibleDetectionController**](src/CollectibleDetectionController.ts) keeps a periodically updated list of ERC-721 tokens assigned to the currently selected address.
 - [**CollectiblesController**](src/CollectiblesController.ts) tracks ERC-721 and ERC-1155 tokens assigned to the currently selected address, using OpenSea to retrieve token information.
 - [**CurrencyRateController**](src/CurrencyRateController.ts) keeps a periodically updated value of the exchange rate from the currently selected "native" currency to another (handling testnet tokens specially).
+- [**RatesController**](src/RatesController/RatesController.ts) keeps a periodically updated value for the exchange rates for different cryptocurrencies. The difference between the `RatesController` and `CurrencyRateController` is that the second one is coupled to the `NetworksController` and is EVM specific, whilst the first one can handle different blockchain currencies like BTC and SOL.
 - [**TokenBalancesController**](src/TokenBalancesController.ts) keeps a periodically updated set of balances for the current set of ERC-20 tokens.
 - [**TokenDetectionController**](src/TokenDetectionController.ts) keeps a periodically updated list of ERC-20 tokens assigned to the currently selected address.
 - [**TokenListController**](src/TokenListController.ts) uses the MetaSwap API to keep a periodically updated list of known ERC-20 tokens along with their metadata.
 - [**TokenRatesController**](src/TokenRatesController.ts) keeps a periodically updated list of exchange rates for known ERC-20 tokens relative to the currently selected native currency.
 - [**TokensController**](src/TokensController.ts) stores the ERC-20 and ERC-721 tokens, along with their metadata, that are listed in the wallet under the currently selected address on the currently selected chain.
 
+### `RatesController`
+
+The `RatesController` is responsible for managing the state related to cryptocurrency exchange rates and periodically updating these rates by fetching new data from an external API.
+
+```ts
+// Initialize the RatesController
+const ratesController = new RatesController({
+  interval: 180000,
+  includeUsdRate: true,
+  state: {
+    fiatCurrency: 'eur',
+    cryptocurrencies: [Cryptocurrency.Btc],
+  },
+});
+
+// Start the polling process
+ratesController.start().then(() => {
+  console.log('Polling for exchange rates has started.');
+});
+
+// Stop the polling process after some time
+setTimeout(() => {
+  ratesController.stop().then(() => {
+    console.log('Polling for exchange rates has stopped.');
+  });
+}, 300000);
+```
+
 ## Contributing
 
 This package is part of a monorepo. Instructions for contributing can be found in the [monorepo README](https://github.com/MetaMask/core#readme).

packages/assets-controllers/src/CurrencyRateController.ts

@@ -14,7 +14,7 @@ import type {
 import { StaticIntervalPollingController } from '@metamask/polling-controller';
 import { Mutex } from 'async-mutex';
 
-import { fetchExchangeRate as defaultFetchExchangeRate } from './crypto-compare';
+import { fetchExchangeRate as defaultFetchExchangeRate } from './crypto-compare-service';
 
 /**
  * @type CurrencyRateState