Fix upper bound assertions to use strict inequality

Change mu_tilde_floyd assertions from <= to < to match the API guarantee
that μ̃ < μ + λ (strict inequality) for floyd_partial.

Co-authored-by: samueltardieu <[email protected]>

Author: Copilot

tests/cycle_detection.rs

@@ -95,7 +95,7 @@ fn test_longer_cycle() {
 
     // Mu_tilde should be valid upper bounds
     assert!(mu_floyd <= mu_tilde_floyd);
-    assert!(mu_tilde_floyd <= mu_floyd + lam_floyd);
+    assert!(mu_tilde_floyd < mu_floyd + lam_floyd);
     assert!(mu_brent <= mu_tilde_brent);
 }
 
@@ -131,6 +131,6 @@ fn test_short_cycle_large_mu() {
 
     // Mu_tilde should be valid upper bounds
     assert!(mu_floyd <= mu_tilde_floyd);
-    assert!(mu_tilde_floyd <= mu_floyd + lam_floyd);
+    assert!(mu_tilde_floyd < mu_floyd + lam_floyd);
     assert!(mu_brent <= mu_tilde_brent);
 }