ludic.physics, ludic.character, ludic.vehicles: fact records reused, and phys_sink allocates nothing

The per-frame sweep over physics, character, vehicles and nav found three fact makers that made a record per fact: contacts and splashes, the character's and the vehicles'. Each keeps a pool now, as wildlife's and npc's do (q_unheld). phys_sink, asked on every removal, built two new lists each time; it filters into a kept spare pair and swaps. ludic.nav's paths and crowds already allocate nothing, and none of the four builds a string per call. What remains at load, reset or a world swap is not per frame. vehicle_feed takes its state mut. vehicles_test: 1000 fed facts, drained turn by turn, use at most 4 records. All packages 421.

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

packages/ludic.character/ports.ludic

@@ -104,6 +104,9 @@ export state CharacterState {
   chr_safe_x: float = 0.0
   chr_safe_z: float = 0.0
   chr_fact_q: Queue<CharacterFact> = chr_fact_q__new()
+  chr_fpool: []CharacterFact = new []CharacterFact   # every fact record made, reused once no drain holds it
+  chr_ffree: []CharacterFact = new []CharacterFact
+  chr_fnext: int = 0
 }
 function chr__top_plain(x: float, z: float, r: float, from_y: float, step: float, base: float) -> float { return base }
 function chr__bed_plain(x: float, z: float) -> float { return CharacterGround.height(x, z) }