chore(engine-ambient): harden shim + LocalLog statics for fixture parallelism

Follow-up to the multi-instancing migration. Wraps the process-shared engine
statics that aren't ambient-fronted but race between concurrent battles:

- UnityEngine.Resources._loaded: Dictionary -> ConcurrentDictionary.GetOrAdd
  (the shared prefab cache keyed by path; concurrent first-misses produced
  duplicate GameObjects + Dictionary corruption)
- UnityEngine.GameObject._components: Dictionary -> ConcurrentDictionary with
  Interlocked.CompareExchange init (Resources.Load returns SHARED prefab
  GameObjects, so two engines' Setup() can race on the same _components map
  — surfaced as "Operations that change non-concurrent collections" crashes
  during BattleManagerBase ctor's GetComponent<T>() chain)
- Wizard.LocalLog: single static lock around all mutating entry points
  (StringBuilder _lastTraceLogStringBuilder + ~12 mutable string/bool/int
  scratch fields; serializing the trace-log surface is cheap since logging
  is not the hot path)

Flips SVSim.BattleEngine.Tests assembly Parallelizable scope from Self to
Fixtures and restructures MultiInstanceEngineTests.StressN_BaselineMatches so
Setup runs INSIDE Task.Run (was previously serialized as a workaround for the
LocalLog races). The fixture is also lifted to ParallelScope.All so the
two-engines and stress tests can run alongside each other.

Suite fully green under fixture parallelism (59/0/2 across 3 consecutive runs);
SVSim.UnitTests still 1054/0/0 — true multi-instance correctness is now proved
end-to-end in tests rather than gated behind a serial workaround.

Manifest sha refresh + new patch artifact for the LocalLog edit (decomp-origin);
the two shim files are authored, so no metadata update is needed for them.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SVSim.BattleEngine/COPIED.manifest.tsv

@@ -2883,7 +2883,7 @@ Wizard\LoadQueue.cs	Wizard\LoadQueue.cs	a3bd987174d57f1e63dc59f67a02235addb16bd5
 Wizard\LoadSceneStoryData.cs	Wizard\LoadSceneStoryData.cs	28456cdcdbc3a76e45d48f88133b868006e40ee12a26509e35707de3c5a0b18a	0
 Wizard\LoadTask.cs	Wizard\LoadTask.cs	6a096260ee3c7b9351e065adb1d491055638bd1646e04d90b203d803434de76e	0
 Wizard\LoadingDownLoadStoryView.cs	Wizard\LoadingDownLoadStoryView.cs	fce928ee1d58540944ceeeb774e8fad892bb968a3265d7a7bde5474574f63c8c	0
-Wizard\LocalLog.cs	Wizard\LocalLog.cs	991b50f5e128fd3b2368770fe7a7b7691ce4090bdaca5ae744d1f464572caab0	0
+Wizard\LocalLog.cs	Wizard\LocalLog.cs	b2ab4a0d1b1025a8a575652cf809b1be4de51ca3a1e5a10314d699516abe2f70	1
 Wizard\LocalizeJson.cs	Wizard\LocalizeJson.cs	4adf1a47af054dc08971d7e8d1574e8b8d7692c027182ff6c3d167164240f4ea	0
 Wizard\LootBoxDialogUtility.cs	Wizard\LootBoxDialogUtility.cs	8277f2e7dfbe98bc4e8790630c338d50a0e635f7566e9d1ee1cd22cd6b199237	0
 Wizard\MailReadTask.cs	Wizard\MailReadTask.cs	cf7a15cf5efb729c839d0ff374d9077dd62151055fc149b44108743efe6d583c	0