Add rustfmt formatting policy and reformat codebase

Add rustfmt.toml with stable defaults and apply cargo fmt to all
source files. This establishes a consistent formatting baseline
for CI enforcement.

src/node/routing_error_rate_limit.rs

@@ -70,7 +70,6 @@ impl RoutingErrorRateLimiter {
     pub fn len(&self) -> usize {
         self.last_sent.len()
     }
-
 }
 
 impl Default for RoutingErrorRateLimiter {