style(server): clear clippy-1.93 cfg(test)/test-target debt (#967)

Manual clippy-1.93 fixes that the prior machine-applicable sweep couldn't auto-
apply, all in cfg(test) modules and tests/ targets (invisible to the lib-only
pre-push clippy, hence accumulated unflagged):

- disallowed_types HashSet/HashMap → BTreeSet/BTreeMap (determinism rule):
  shadowcast_bench.rs (×8, (i32,i32) keys), mood.rs, sound.rs. SoundEventKind
  gains a PartialOrd/Ord derive (fieldless Copy enum) so it is BTree-usable.
- field_reassign_with_default → struct-init: disclosure.rs, monologue.rs (×2),
  save_io.rs (keeps `mut` for the deliberate last-write-wins overwrite).
- assertions_on_constants on the EAVESDROP_THRESHOLD invariant → compile-time
  `const _: () = assert!(...)`: listening.rs, cross_room_transitions.rs. This is
  stronger than the runtime assert and needs no #[allow].
- approx_constant: settings/types.rs round-trip literal 3.14 → 2.5 (the value is
  arbitrary test data, never meant to be PI — change avoids both the lint and a
  suppression).
- drop_non_drop: vision.rs early Mut<WalkabilityMap> release → scoped block.
- unnecessary_get_then_check → contains_key: information_boundaries.rs (×3).
- cloned_ref_to_slice_refs → std::slice::from_ref: triangle_validation.rs.
- unused_must_use: input.rs dropped the unused .id() on a spawn.

cargo clippy --all-targets -- -D warnings is clean; cargo test green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/tests/cross_room_transitions.rs

@@ -641,8 +641,6 @@ fn t8_sprint_blocks_eavesdrop_then_careful_enables_accumulation() {
     }
 
     // Verify D-071 invariant: Careful threshold is strictly less than normal.
-    assert!(
-        EAVESDROP_THRESHOLD_CAREFUL < EAVESDROP_THRESHOLD,
-        "T8: Careful threshold must be < normal threshold (D-071 invariant)"
-    );
+    // Compile-time invariant — pins the ordering against a future const edit.
+    const _: () = assert!(EAVESDROP_THRESHOLD_CAREFUL < EAVESDROP_THRESHOLD);
 }

server/tests/information_boundaries.rs

@@ -59,7 +59,7 @@ fn player_kg_has_no_passive_npc_leakage() {
 
     // Negative assertion: a freshly created KG contains no entity references.
     assert!(
-        player_kg.entities.get(&npc_id).is_none(),
+        !player_kg.entities.contains_key(&npc_id),
         "IB-1: fresh KnowledgeGraph must not contain any entity (passive leakage — D-010 principle 2)"
     );
     assert!(
@@ -78,7 +78,7 @@ fn player_kg_has_no_passive_npc_leakage() {
     // Player's KG must be empty regardless of NPCs existing nearby.
     let kg = world.get::<KnowledgeGraph>(player).unwrap();
     assert!(
-        kg.entities.get(&npc_id).is_none(),
+        !kg.entities.contains_key(&npc_id),
         "IB-1: spawning an NPC in the world must not passively populate the player's KG"
     );
     assert!(
@@ -249,7 +249,7 @@ fn save_state_npc_kg_isolation() {
     // NPC_A's KG entry for NPC_B is NPC_A's OBSERVATION DATA (where NPC_A saw NPC_B).
     // This is not NPC_B's own KG — it's NPC_A's record of NPC_B's position.
     assert!(
-        kg.entities.get(&npc_b_id).is_some(),
+        kg.entities.contains_key(&npc_b_id),
         "IB-4 sanity: NPC_A's KG should still contain its observation of NPC_B after roundtrip"
     );
 }

server/tests/shadowcast_bench.rs

@@ -7,7 +7,7 @@ use rand::Rng;
 use rand::SeedableRng;
 use rand_chacha::ChaCha8Rng;
 use settled_reach_server::perception::shadowcast::{recursive_shadowcast, symmetric_shadowcast};
-use std::collections::HashSet;
+use std::collections::BTreeSet;
 use std::time::Instant;
 
 /// Configuration for a benchmark run
@@ -20,9 +20,9 @@ struct BenchConfig {
 }
 
 /// Generate a random wall map with specified density
-fn generate_wall_map(size: i32, density: f64, seed: u64) -> HashSet<(i32, i32)> {
+fn generate_wall_map(size: i32, density: f64, seed: u64) -> BTreeSet<(i32, i32)> {
     let mut rng = ChaCha8Rng::seed_from_u64(seed);
-    let mut walls = HashSet::new();
+    let mut walls = BTreeSet::new();
 
     for x in 0..size {
         for y in 0..size {
@@ -203,7 +203,7 @@ fn symmetric_algorithm_is_symmetric() {
     println!("\n=== Testing Symmetric Property (simplified) ===\n");
 
     // Simple open field test - perfect symmetry should hold here
-    let no_walls: HashSet<(i32, i32)> = HashSet::new();
+    let no_walls: BTreeSet<(i32, i32)> = BTreeSet::new();
     let is_opaque = |x: i32, y: i32| no_walls.contains(&(x, y));
 
     let test_positions = vec![(0, 0), (3, 3), (5, 2), (1, 7)];
@@ -246,14 +246,14 @@ fn both_algorithms_agree_on_basic_cases() {
     println!("\n=== Comparing Algorithm Results ===\n");
 
     let test_cases = vec![
-        ("Open field", HashSet::new()),
+        ("Open field", BTreeSet::new()),
         ("Single wall at (2,0)", {
-            let mut w = HashSet::new();
+            let mut w = BTreeSet::new();
             w.insert((2, 0));
             w
         }),
         ("L-shaped corridor", {
-            let mut w = HashSet::new();
+            let mut w = BTreeSet::new();
             for i in 0..5 {
                 w.insert((i, 2));
                 w.insert((2, i));

server/tests/triangle_validation.rs

@@ -390,7 +390,7 @@ fn triangle_validation_cross_template_deterministic() {
         &mut world1,
         hub_id,
         bar_id,
-        &[overridden.clone()],
+        std::slice::from_ref(&overridden),
         &mut SimRng::new(42),
     );