ludic.base, ludic.wildlife, ludic.npc: fact records reused, not made per fact

wl_fact made a new WildFact per fact, about one a frame, and Ludic never gives one back. ludic.base's q_unheld(q, pool, out) lists the records a queue no longer holds: neither waiting nor handed out by its last drain, which is good until the next drain. ludic.wildlife and ludic.npc now keep a pool, hand out a free record, and make a new one only when every record is held. Taking a record writes the state, so wl_fact / np_fact and the few callers holding their state read-only take it mut. Tests: q_unheld's rules (an empty drain holds on, the safe side); 3000 prints drained frame by frame use at most 4 records; 500 arrivals drained turn by turn use at most 4. base 37, wildlife 27, npc 17; all packages 420.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.npc/tests/way_test.ludic

@@ -101,4 +101,20 @@ program NpcWayTest {
     expect_eq(p.act, NPCA_SIT)
     expect(p.phase > 100.0)
   }
+
+  test "an arrival a turn, drained each turn, makes a few fact records and then reuses them" (npc_st: mut NpcState, npc_tests_fake_st: mut NpcTestsFakeState, way_test_st: WayTestState) {
+    fk_setup(npc_st, npc_tests_fake_st)
+    npc_tests_fake_st.fk_want = 1
+    let p = npc_spawn(npc_st, NPCK_HIKER)
+    var arrived = 0
+    for k in 0 .. 500 {
+      npc_set_at(p, 0.0, 0.0)
+      npc_go(npc_st, p, 0.5, 0.0, NPCA_SIT, 30.0)
+      npc_tick(npc_st, 0.05)
+      let fs = q_drain(npc_facts(npc_st))
+      for i in 0 .. len(fs) { if fs[i].what == NPC_F_ARRIVED { arrived += 1 } }
+    }
+    expect(arrived > 400)
+    expect(npc_fact_records(npc_st) <= 4)
+  }
 }