[Bug] Added timezone to latest speedtest API response

[alexjustesen]

📃 Description

This PR adds display timezone to the /speedtest/latest API response. Expands on the work started in #1070.

Before

{
    "message":"ok",
    "data":{
        "id":1,
        "created_at":"2024-04-10T01:41:12.000000+00:00",
        "updated_at":"2024-04-10T01:41:33.000000+00:00"
    }
}

After

{
    "message":"ok",
    "data":{
        "id":1,
        "created_at":"2024-04-09T21:41:12.000000-04:00",
        "updated_at":"2024-04-09T21:41:33.000000-04:00"
    }
}

• closes Time/date doesn't seem to respect timezone in API requests #1375

🪵 Changelog

🔧 Fixed

• added display timezone to latest speedtest API response