Allow for configurable Session Storage

[nicknisi]

Replace Cookie Singleton with SessionStorageManager

Overview

This PR replaces our current cookie singleton approach with a more flexible and testable SessionStorageManager class. The key changes:

1. Remove cookie.ts in favor of a new sessionStorage.ts module
2. Introduce SessionStorageManager class to handle session storage configuration
3. Support custom session storage/cookie configurations
4. Improve handling of concurrent session configuration in Remix's parallel loader environment

Key Changes

• Removed direct cookie singleton export in favor of configureSessionStorage and getSessionStorage functions
• Added SessionStorageManager class with proper promise-based configuration handling
• Extended AuthKitLoaderOptions to support custom storage and cookie configurations
• Improved race condition handling for parallel loader execution
• Updated tests to match new architecture

Example Usage

// in root.tsx
const cookie = createCookie("_session", {
  path: "/",
  httpOnly: true,
  secure: isSecureProtocol,
  sameSite: "lax",
  maxAge: 60 * 60 * 24 * 400,
  secrets: [
    process.env.WORKOS_COOKIE_PASSWORD
  ],
});

export const loader = (args: LoaderFunctionArgs) =>
  authkitLoader(
    args,
    async () => {
      return json({
        signInUrl: await getSignInUrl(),
      });
    },
    {
      debug: true,
      cookie,
      storage: createMemorySessionStorage({
        cookie,
      }),
    }
  );

Fixes #2