Add retry option to configure backoff limit

The default backoff function is exponential, so after a couple of retries the delay will become very large.
In case you are polling an api, you want at least that there is an upper limit to this delay, for example 1000ms.

source/core/Ky.ts

@@ -218,7 +218,7 @@ export class Ky {
 			}
 
 			const BACKOFF_FACTOR = 0.3;
-			return BACKOFF_FACTOR * (2 ** (this._retryCount - 1)) * 1000;
+			return Math.min(this._options.retry.backoffLimit, BACKOFF_FACTOR * (2 ** (this._retryCount - 1)) * 1000);
 		}
 
 		return 0;

source/types/retry.ts

@@ -33,4 +33,16 @@ export interface RetryOptions {
 	@default Infinity
 	*/
 	maxRetryAfter?: number;
+
+	/**
+	The upper limit of the `computedValue`.
+
+	By default, the computedValue is calculated in the following way:
+
+	0.3 * (2 ** (attemptCount - 1)) * 1000
+
+	The delay increases exponentially.
+	In order to prevent this, you can set this value to a fixed value, such as 1000.
+	 */
+	backoffLimit?: number;
 }

source/utils/normalize.ts

@@ -17,6 +17,7 @@ const defaultRetryOptions: Required<RetryOptions> = {
 	statusCodes: retryStatusCodes,
 	afterStatusCodes: retryAfterStatusCodes,
 	maxRetryAfter: Number.POSITIVE_INFINITY,
+	backoffLimit: Number.POSITIVE_INFINITY,
 };
 
 export const normalizeRetryOptions = (retry: number | RetryOptions = {}): Required<RetryOptions> => {