Added test package in nix flake to automatically run tests.

To be able to do such, it was required to add the vendor directory
to the git project.

vendor/deno.land/x/base64@v0.2.1/base64url.ts

@@ -0,0 +1,17 @@
+import { init } from "./base.ts";
+
+const lookup: string[] = [];
+const revLookup: number[] = [];
+const code: string =
+  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+
+for (let i: number = 0, l = code.length; i < l; ++i) {
+  lookup[i] = code[i];
+  revLookup[code.charCodeAt(i)] = i;
+}
+
+export const { byteLength, toUint8Array, fromUint8Array } = init(
+  lookup,
+  revLookup,
+  true,
+);