Fix asset deletion flow and async loading race conditions

[Copilot]

Review and fix correctness issues in the asset deletion pipeline and async loading flow, covering a compile-error-level capture bug, a double-load race, missing cache eviction on deletion, and several null-deref hazards.

Async Loading (AssetManager::LoadAsset)

• Lambda capture bug (compile error): The previous fix introduced asset->status.store(FAILED) inside a lambda whose capture list was [this, uuid, archive, deps=...] — asset was never captured. Replaced with FindAsset(uuid) via the already-captured this:

  // Before — `asset` not in capture list, compile error
  if (!success) { asset->status.store(AssetBase::Status::FAILED); return; }
  
  // After
  if (!success) {
      auto failedAsset = FindAsset(uuid);
      if (failedAsset) { failedAsset->status.store(AssetBase::Status::FAILED); }
      return;
  }

• LOADING-state race: The early-return guard only checked IsLoaded(). A concurrent second call for the same UUID would fall through, re-open the file, and queue a duplicate async task. Now short-circuits for both LOADED and LOADING.

Asset Deletion

• AssetDataBase::RemoveAsset: Replaced SKY_ASSERT(idMap.count(id)) with a graceful iterator-based early return. After removing from the source database, now calls AssetManager::RemoveAsset(id) to keep the runtime cache consistent.
• New AssetManager::RemoveAsset(uuid): Evicts the weak_ptr entry under the mutex, then broadcasts IAssetEvent::OnAssetReset to all registered listeners.

Misc

• AssetManager::FindAsset lazily erases expired weak_ptr entries on lookup (marked assets map mutable to allow this in the const method).
• Added null guards to AssetDataBase::OpenFile (both overloads) and CreateOrOpenFile — GetFileSystemBySourcePath returns null for invalid bundle types.

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