refactor(peer): split bulk request dispatch

Move file-chunk and Stream Install branches into focused helpers so the new admission path remains within the workspace's strict Clippy limits without changing request behavior.

Test Plan:
- just clippy
- git diff --check

crates/lanspread-peer/src/services/server.rs

@@ -430,8 +430,7 @@ async fn run_server_body(
 
                     if !has_child_capacity(connection_tasks.len(), MAX_ESTABLISHED_CONNECTIONS) {
                         log::warn!(
-                            "Closing excess peer connection from {remote_addr} at application limit {}",
-                            MAX_ESTABLISHED_CONNECTIONS,
+                            "Closing excess peer connection from {remote_addr} at application limit {MAX_ESTABLISHED_CONNECTIONS}",
                         );
                         connection.close(application::Error::UNKNOWN);
                         continue;