perf: resolve global lock contention in template server

[idogrady]

Replaces the global RwLock over the server sessions map with dashmap to provide highly concurrent bucket-level sharding. This removes the latency bottleneck where single ingest requests would block all other sessions. Fine-grained locking has also been added to SessionEntry.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR updates the example server’s session storage to improve concurrency by replacing a globally locked HashMap with DashMap and moving locking to per-session fields.

Changes:

• Replace Arc<RwLock<HashMap<...>>> session store with Arc<DashMap<...>>.
• Introduce per-session synchronization (RwLock for template index, Mutex for last-touch timestamp).
• Update routes and TTL sweeper to operate on the new session store.

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
examples/server/tests/integration.rs	Updates test state construction to use DashMap sessions.
examples/server/src/session.rs	Changes AppState.sessions type and adds per-session locks.
examples/server/src/routes.rs	Adjusts session lookup/insert and per-session locking around index/last_touch.
examples/server/src/main.rs	Updates TTL sweeper to retain entries directly in DashMap.
examples/server/Cargo.toml	Adds dashmap dependency.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.