Mod: Do LayeredFs loading Parallel to improve speed (#6180)

* Mod: Do LayeredFs loading Parallel to improve speed

This fixes and superseed #5672 due to inactivity, nothing more.
(See original PR for description)

Testing are welcome.

Close #5661

* Addresses gdkchan's feedback

* commit to test mako change

* Revert "commit to test mako change"

This reverts commit 8b0caa8a21db298db3dfcbe5b7e9029c4f066c46.

src/Ryujinx.HLE/HOS/Services/Fs/FileSystemProxy/LazyFile.cs

@@ -0,0 +1,65 @@
+using LibHac;
+using LibHac.Common;
+using LibHac.Fs;
+using System;
+using System.IO;
+
+namespace Ryujinx.HLE.HOS.Services.Fs.FileSystemProxy
+{
+    class LazyFile : LibHac.Fs.Fsa.IFile
+    {
+        private readonly LibHac.Fs.Fsa.IFileSystem _fs;
+        private readonly string _filePath;
+        private readonly UniqueRef<LibHac.Fs.Fsa.IFile> _fileReference = new();
+        private readonly FileInfo _fileInfo;
+
+        public LazyFile(string filePath, string prefix, LibHac.Fs.Fsa.IFileSystem fs)
+        {
+            _fs = fs;
+            _filePath = filePath;
+            _fileInfo = new FileInfo(prefix + "/" + filePath);
+        }
+
+        private void PrepareFile()
+        {
+            if (_fileReference.Get == null)
+            {
+                _fs.OpenFile(ref _fileReference.Ref, _filePath.ToU8Span(), OpenMode.Read).ThrowIfFailure();
+            }
+        }
+
+        protected override Result DoRead(out long bytesRead, long offset, Span<byte> destination, in ReadOption option)
+        {
+            PrepareFile();
+
+            return _fileReference.Get!.Read(out bytesRead, offset, destination);
+        }
+
+        protected override Result DoWrite(long offset, ReadOnlySpan<byte> source, in WriteOption option)
+        {
+            throw new NotSupportedException();
+        }
+
+        protected override Result DoFlush()
+        {
+            throw new NotSupportedException();
+        }
+
+        protected override Result DoSetSize(long size)
+        {
+            throw new NotSupportedException();
+        }
+
+        protected override Result DoGetSize(out long size)
+        {
+            size = _fileInfo.Length;
+
+            return Result.Success;
+        }
+
+        protected override Result DoOperateRange(Span<byte> outBuffer, OperationId operationId, long offset, long size, ReadOnlySpan<byte> inBuffer)
+        {
+            throw new NotSupportedException();
+        }
+    }
+}