feat: new router and benchmark setup

src/router/cache_affinity.rs

@@ -59,39 +59,39 @@ pub struct CacheAffinityRouter {
 }
 
 impl CacheAffinityRouter {
-    pub fn new(load_alpha: f64) -> Self {
+    pub fn new(load_alpha: f64, fingerprint_k: usize) -> Self {
         Self {
             name: "cache_affinity",
             load_alpha,
             l0_gamma: 1.0,
             meta_delta: 0.25,
-            fingerprint_k: 4,
+            fingerprint_k: fingerprint_k.max(1),
             use_rendezvous: true,
         }
     }
 
     /// Ablation: cache_score-style weights (γ=0.1, δ=0) but keep rendezvous
     /// tiebreak. Isolates the contribution of deterministic sticky placement.
-    pub fn weak_with_rendezvous(load_alpha: f64) -> Self {
+    pub fn weak_with_rendezvous(load_alpha: f64, fingerprint_k: usize) -> Self {
         Self {
             name: "cache_affinity_weak_rend",
             load_alpha,
             l0_gamma: 0.1,
             meta_delta: 0.0,
-            fingerprint_k: 4,
+            fingerprint_k: fingerprint_k.max(1),
             use_rendezvous: true,
         }
     }
 
     /// Ablation: strong cache weights (γ=1.0, δ=0.25) but first-found tiebreak
     /// instead of rendezvous. Isolates the contribution of reweighting alone.
-    pub fn strong_no_rendezvous(load_alpha: f64) -> Self {
+    pub fn strong_no_rendezvous(load_alpha: f64, fingerprint_k: usize) -> Self {
         Self {
             name: "cache_affinity_strong_only",
             load_alpha,
             l0_gamma: 1.0,
             meta_delta: 0.25,
-            fingerprint_k: 4,
+            fingerprint_k: fingerprint_k.max(1),
             use_rendezvous: false,
         }
     }