feat(render): unify physical residency accounting

src/AcDream.Content/IPreparedAssetSource.cs

@@ -119,6 +119,12 @@ public interface IPreparedAssetSource : IDisposable
     PreparedAssetSourceStats Stats { get; }
 
     CacheStats DecodedTextureCacheStats { get; }
+
+    /// <summary>
+    /// Immutable package address-space mapped by this source. This is virtual
+    /// address space, not committed managed or process-working-set bytes.
+    /// </summary>
+    long MappedVirtualBytes => 0;
 }
 
 internal static class PreparedAssetRequestContract
@@ -211,6 +217,8 @@ public sealed class PakPreparedAssetSource : IPreparedAssetSource
 
     public CacheStats DecodedTextureCacheStats => default;
 
+    public long MappedVirtualBytes => _reader.FileLength;
+
     public PreparedAssetPresence Probe(
         PakAssetType type,
         uint sourceFileId)

src/AcDream.Content/Pak/PakReader.cs

@@ -46,6 +46,7 @@ public sealed class PakReader : IDisposable {
     private readonly ConcurrentDictionary<int, bool> _loggedCorruption = new();
 
     public PakHeader Header { get; }
+    public long FileLength => _fileLength;
 
     public PakReader(string path) {
         _fileLength = new FileInfo(path).Length;