Function pod_root_url 

pub fn pod_root_url(pod_base: &str, pubkey: &str) -> String

Root URL of a per-user pod: {pod_base}/pods/{pubkey}/.

pod_base is taken verbatim — callers should pass the value of [pod].base_url (e.g. https://pods.example.com). The pubkey is the hex-encoded BIP-340 x-only key.