feat(rest): callbacks for timeout and retry backoff (#11067)

* feat(rest): callbacks for timeout and retry backoff

* test: add tests for callback utils

* test: fix typo

Co-authored-by: Qjuh <76154676+Qjuh@users.noreply.github.com>

* fix(retryBackoff): efficient math

* docs: minor tweaks

* docs: captalisation

---------

Co-authored-by: Qjuh <76154676+Qjuh@users.noreply.github.com>
Co-authored-by: Jiralite <33201955+Jiralite@users.noreply.github.com>

packages/rest/__tests__/BurstHandler.test.ts

@@ -16,6 +16,7 @@ const api = new REST();
 
 let mockAgent: MockAgent;
 let mockPool: Interceptable;
+let serverOutage = true;
 
 beforeEach(() => {
 	mockAgent = new MockAgent();
@@ -138,3 +139,57 @@ test('Handle unexpected 429', async () => {
 	expect(await unexpectedLimit).toStrictEqual({ test: true });
 	expect(performance.now()).toBeGreaterThanOrEqual(previous + 1_000);
 });
+
+test('server responding too slow', async () => {
+	const api2 = new REST({ timeout: 1 }).setToken('A-Very-Really-Real-Token');
+
+	api2.setAgent(mockAgent);
+
+	mockPool
+		.intercept({
+			path: callbackPath,
+			method: 'POST',
+		})
+		.reply(200, '')
+		.delay(100)
+		.times(10);
+
+	const promise = api2.post('/interactions/1234567890123456789/totallyarealtoken/callback', {
+		auth: false,
+		body: { type: 4, data: { content: 'Reply' } },
+	});
+
+	await expect(promise).rejects.toThrowError('aborted');
+}, 1_000);
+
+test('Handle temp server outage', async () => {
+	mockPool
+		.intercept({
+			path: callbackPath,
+			method: 'POST',
+		})
+		.reply(() => {
+			if (serverOutage) {
+				serverOutage = false;
+
+				return {
+					statusCode: 500,
+					data: '',
+				};
+			}
+
+			return {
+				statusCode: 200,
+				data: { test: true },
+				responseOptions,
+			};
+		})
+		.times(2);
+
+	expect(
+		await api.post('/interactions/1234567890123456789/totallyarealtoken/callback', {
+			auth: false,
+			body: { type: 4, data: { content: 'Reply' } },
+		}),
+	).toStrictEqual({ test: true });
+});