Add ConfigServiceImpl and ConfigProtocol irpc enum behind feature flag

ConfigServiceImpl wraps ArcSwap<DynamicConfig> providing forwarding_policy(),
rate_limits(), and reload() methods for direct use (always available).
ConfigProtocol enum (GetForwardingPolicy, GetRateLimits, ReloadForwarding,
ReloadRateLimits) is gated behind the irpc feature flag per ADR-030.

crates/alknet-core/Cargo.toml

@@ -14,6 +14,7 @@ default = []
 tls = ["dep:tokio-rustls", "dep:rustls", "dep:rustls-pki-types", "dep:webpki-roots"]
 iroh = ["dep:iroh", "dep:url"]
 acme = ["dep:rustls-acme", "dep:futures", "tls"]
+irpc = []
 testutil = []
 transport-traits = []