modules: split services and the ircd link into external crates

nickserv, chanserv and the InspIRCd protocol move out of the binary into their
own workspace crates (fedserv-nickserv, fedserv-chanserv, fedserv-inspircd),
each depending only on fedserv-api. human_time and the branded account emails
move into the SDK crate so a module needs nothing from core; the engine keeps
its own inherent methods and builds emails via fedserv-api too. The bin now
constructs each module from its crate instead of an in-tree #[path] include.
Proves the SDK is self-sufficient: a third-party module is the same shape.

src/grpc.rs

@@ -316,7 +316,7 @@ pub async fn run(engine: Shared, cfg: GrpcCfg, outbound: broadcast::Sender<LogEn
 mod tests {
     use super::*;
     use crate::engine::db::Db;
-    use crate::nickserv::NickServ;
+    use fedserv_nickserv::NickServ;
     use tokio_stream::StreamExt;
     use tonic::metadata::MetadataValue;