fix: auth route handlers not ending correctly

[mohd-akram]

The missing return in the protected routes handler caused the request to continue processing even after the redirect, leading to this error:

Error [ERR_HTTP_HEADERS_SENT]: Cannot write headers after they are sent to the client
    at ServerResponse.writeHead (node:_http_server:345:11)
    at safeWriteHead (/Users/user/code/project/node_modules/fastify/lib/reply.js:572:9)
    at onSendEnd (/Users/user/code/project/node_modules/fastify/lib/reply.js:621:5)
    at wrapOnSendEnd (/Users/user/code/project/node_modules/fastify/lib/reply.js:565:5)
    at next (/Users/user/code/project/node_modules/fastify/lib/hooks.js:289:7)
    at Object.fastifyCookieOnSendHandler (/Users/user/code/project/node_modules/@fastify/cookie/plugin.js:113:3)
    at next (/Users/user/code/project/node_modules/fastify/lib/hooks.js:295:30)
    at /Users/user/code/project/node_modules/@fastify/session/lib/fastifySession.js:201:9
    at Immediate._onImmediate (/Users/user/code/project/node_modules/@fastify/session/lib/session.js:180:11)
    at process.processImmediate (node:internal/timers:480:21) {
  code: 'ERR_HTTP_HEADERS_SENT'
}

Add returns to other async handlers too as is recommended.

[mohd-akram]

Is this good to merge? See the promise resolution section in the docs for more info on this.

[github-actions[bot]]

:tada: This PR is included in version 4.1.2 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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