Open Route 30 with map trainers and multi-Pokémon trainer battles

Map trainers run the ROM's TalkToTrainerScript and SeenByTrainerScript.
_CheckTrainerBattle runs before tile events at the end of each step and
on idle ticks; TrainerWalkToPlayer builds wMovementBuffer natively, and
writeobjectxy keeps the trainer where it stopped. The interpreter gains
the trainer header commands, wRunningTrainerBattleScript and hidden
items (HiddenItemScript).

Trainers with several Pokémon send out the next one through
EnemyPartyMonEntrance and FindMonInOTPartyToSwitchIntoBattle, including
its BattleRandom fallback. AI_SwitchOrTryItem, CheckAbleToSwitch and
AI_Switch are translated with their original bugs, and wPlayerUsedMoves
is recorded. The Shift-mode switch offer, trainer items, Pursuit on a
switch, Perish Song and Spikes remain refused.

Route 30 and its Berry house are enabled; Mr. Pokémon's house and
Route 31 stay closed. A refused trainer sighting does not restart until
the player moves, so a rollback cannot trap the player in view.

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

tests/trainer-walk.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, it } from "vitest";
+import { trainerWalkBuffer } from "../src/game/scripts/interpreter";
+import { readMovement } from "../src/game/scripts/movement";
+
+describe("TrainerWalkToPlayer", () => {
+  const decode = (buffer: number[]) => readMovement({ byte: (index) => buffer[index] }, 0);
+  it("only pauses when the player is adjacent", () => {
+    expect(trainerWalkBuffer({ x: 5, y: 5 }, { x: 5, y: 6 }, 1)).toEqual([0x3e, 0x47]);
+    expect(decode([0x3e, 0x47])).toEqual([{ kind: "sleep", ticks: 1 }]);
+  });
+  it("walks all but the last tile toward the player at normal speed", () => {
+    // step DOWN is movement_step | DOWN.
+    expect(trainerWalkBuffer({ x: 1, y: 7 }, { x: 1, y: 10 }, 3)).toEqual([0x3e, 0x0c, 0x0c, 0x47]);
+    expect(trainerWalkBuffer({ x: 9, y: 4 }, { x: 4, y: 4 }, 5)).toEqual([0x3e, 0x0e, 0x0e, 0x0e, 0x0e, 0x47]);
+    expect(trainerWalkBuffer({ x: 2, y: 4 }, { x: 4, y: 4 }, 2)).toEqual([0x3e, 0x0f, 0x47]);
+    expect(decode([0x3e, 0x0d, 0x47])).toEqual([
+      { kind: "sleep", ticks: 1 },
+      { kind: "step", direction: "up", ticks: 8, animate: true },
+    ]);
+  });
+  it("follows ComputePathToWalkToPlayer off a straight line: the shorter axis first", () => {
+    expect(trainerWalkBuffer({ x: 0, y: 0 }, { x: 3, y: 1 }, 4)).toEqual([0x3e, 0x0c, 0x0f, 0x0f, 0x47]);
+  });
+});