fix: process first call to update the rates controller then start polling (#5364)

## Explanation
We observed that once the rate controller is initialized, polling does
not begin until the default interval of three minutes has passed,
causing the rate to only be retrieved after that delay. This leads to a
suboptimal user experience. This pull request addresses the issue by
manually triggering a rate update.

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## References

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### `@metamask/assets-controllers`

- **FIXED**: Resolved an issue where rate polling would only begin after
the default 3-minute interval by manually triggering a rate update upon
initialization, ensuring an immediate refresh for a better user
experience


## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've highlighted breaking changes using the "BREAKING" category
above as appropriate
- [ ] I've prepared draft pull requests for clients and consumer
packages to resolve any breaking changes

Author: salimtb

packages/assets-controllers/src/RatesController/RatesController.test.ts

@@ -170,7 +170,7 @@ describe('RatesController', () => {
       const ratesPosUpdate = ratesController.state.rates;
 
       // checks for the RatesController:stateChange event
-      expect(publishActionSpy).toHaveBeenCalledTimes(2);
+      expect(publishActionSpy).toHaveBeenCalledTimes(3);
       expect(fetchExchangeRateStub).toHaveBeenCalled();
       expect(ratesPosUpdate).toStrictEqual({
         btc: {
@@ -283,27 +283,27 @@ describe('RatesController', () => {
 
       await advanceTime({ clock, duration: 200 });
 
-      expect(fetchExchangeRateStub).toHaveBeenCalledTimes(1);
+      expect(fetchExchangeRateStub).toHaveBeenCalledTimes(2);
 
       await ratesController.stop();
 
       // check the 3rd call since the 2nd one is for the
       // event stateChange
       expect(publishActionSpy).toHaveBeenNthCalledWith(
-        3,
+        4,
         `${ratesControllerName}:pollingStopped`,
       );
 
       await advanceTime({ clock, duration: 200 });
 
-      expect(fetchExchangeRateStub).toHaveBeenCalledTimes(1);
+      expect(fetchExchangeRateStub).toHaveBeenCalledTimes(2);
 
       await ratesController.stop();
 
       // check if the stop method is called again, it returns early
       // and no extra logic is executed
       expect(publishActionSpy).not.toHaveBeenNthCalledWith(
-        4,
+        3,
         `${ratesControllerName}:pollingStopped`,
       );
     });

packages/assets-controllers/src/RatesController/RatesController.ts

@@ -167,6 +167,8 @@ export class RatesController extends BaseController<
 
     this.messagingSystem.publish(`${name}:pollingStarted`);
 
+    await this.#updateRates();
+
     this.#intervalId = setInterval(() => {
       this.#executePoll().catch(console.error);
     }, this.#intervalLength);