Add stats printing for ReactiveLiveness collections

Print roots, edges, and live (fixpoint) stats in timing mode.

Example output (benchmark, cold start):
ReactiveLiveness collection stats:
  roots: recv=156200 emit=156200 len=16203
  edges: recv=445363 emit=445363 len=35550
  live (fixpoint): recv=601563 emit=107025 len=31903

Key insights:
- fixpoint receives 601,563 updates (roots + edges combined)
- fixpoint emits 107,025 updates (BFS expansion deltas)
- 31,903 positions are live (17,500 decls + type positions)
- On cache hit (run 2), counters stay same = zero new work

Author: cristianoc

analysis/reanalyze/src/ReactiveLiveness.ml

@@ -113,3 +113,15 @@ let create ~(merged : ReactiveMerge.t) : t =
   (* Step 4: Compute fixpoint - all reachable positions from roots *)
   let live = Reactive.fixpoint ~init:all_roots ~edges () in
   {live; edges; roots = all_roots}
+
+(** Print reactive collection update statistics *)
+let print_stats ~(t : t) : unit =
+  let print name (c : _ Reactive.t) =
+    let s = Reactive.stats c in
+    Printf.eprintf "  %s: recv=%d emit=%d len=%d\n" name s.updates_received
+      s.updates_emitted (Reactive.length c)
+  in
+  Printf.eprintf "ReactiveLiveness collection stats:\n";
+  print "roots" t.roots;
+  print "edges" t.edges;
+  print "live (fixpoint)" t.live

analysis/reanalyze/src/ReactiveLiveness.mli

@@ -17,3 +17,6 @@ val create : merged:ReactiveMerge.t -> t
     - roots: initial live positions (annotated + externally referenced)
     
     Updates automatically when any input changes. *)
+
+val print_stats : t:t -> unit
+(** Print update statistics for liveness collections (roots, edges, live fixpoint) *)

analysis/reanalyze/src/Reanalyze.ml

@@ -245,7 +245,7 @@ let shuffle_list lst =
   Array.to_list arr
 
 let runAnalysis ~dce_config ~cmtRoot ~reactive_collection ~reactive_merge
-    ~reactive_liveness:_ ~reactive_solver =
+    ~reactive_liveness ~reactive_solver =
   (* Map: process each file -> list of file_data *)
   let {dce_data_list; exception_results} =
     processCmtFiles ~config:dce_config ~cmtRoot ~reactive_collection
@@ -415,6 +415,9 @@ let runAnalysis ~dce_config ~cmtRoot ~reactive_collection ~reactive_merge
                 ((t1 -. t0) *. 1000.0)
                 ((t2 -. t1) *. 1000.0)
                 num_dead num_live (List.length all_issues);
+              (match reactive_liveness with
+              | Some liveness -> ReactiveLiveness.print_stats ~t:liveness
+              | None -> ());
               ReactiveSolver.print_stats ~t:solver);
             Some (AnalysisResult.add_issues AnalysisResult.empty all_issues)
           | None ->