perf(router): avoid path-param HashMap allocation for static routes

[ZhuchkaTriplesix]

Context

• match_route_compiled in src/state.rs always allocates HashMap<String, String> for path params, even when the route has no :param segments.

Problem

Static routes (the majority in many APIs) pay for an empty HashMap allocation on every request.

Proposed change

• Return (idx, Option<PathParams>) or use a static empty sentinel / SmallVec for 0–2 params.
• Avoid HashMap::new() when matchit params iterator is empty.

Files

• src/state.rs, src/dispatch.rs, call sites in WebSocket matching

Acceptance criteria

• Routing behaviour unchanged for parameterized and static routes.
• Unit tests for static and dynamic paths.
• Optional microbench shows fewer allocations per match.

Expected low-level impact

Fewer heap allocations on every matched static route.