Use crypto.getRandomValues for both Node and browsers

Removes Node/browser-specific PRNGs, since
crypto.getRandomValues is now available in Node.

packages/random/source/system.ts

@@ -1,39 +1,29 @@
-// Copyright (C) 2016 Dmitry Chestnykh
+// Copyright (C) 2024 Dmitry Chestnykh
 // MIT License. See LICENSE file for details.
 
 import { RandomSource } from "./";
-import { BrowserRandomSource } from "./browser";
-import { NodeRandomSource } from "./node";
+
+const QUOTA = 65536;
 
 export class SystemRandomSource implements RandomSource {
     isAvailable = false;
-    name = "";
-    private _source: RandomSource;
+    isInstantiated = false;
 
     constructor() {
-        // Try browser.
-        this._source = new BrowserRandomSource();
-        if (this._source.isAvailable) {
-            this.isAvailable = true;
-            this.name = "Browser";
-            return;
-        }
-
-        // If no browser source, try Node.
-        this._source = new NodeRandomSource();
-        if (this._source.isAvailable) {
+        if (crypto !== undefined && 'getRandomValues' in crypto) {
             this.isAvailable = true;
-            this.name = "Node";
-            return;
+            this.isInstantiated = true;
         }
-
-        // No sources, we're out of options.
     }
 
     randomBytes(length: number): Uint8Array {
         if (!this.isAvailable) {
             throw new Error("System random byte generator is not available.");
         }
-        return this._source.randomBytes(length);
+        const out = new Uint8Array(length);
+        for (let i = 0; i < out.length; i += QUOTA) {
+            crypto.getRandomValues(out.subarray(i, i + Math.min(out.length - i, QUOTA)));
+        }
+        return out;
     }
 }