Complete SC5/SV5 round-trip serialization and editor support in ObjectEditor

[Copilot]

This updates the partial SC5/SV5 implementation to support reliable load/save round-tripping for OpenLoco map files, including packed object chunks and tile-element data. It also fills key S5 structure gaps and wires map-file editing paths needed by the editor UI.

• S5 binary model + serializer parity

  • Completed SCV5 write-path support for packed objects (S5Header + ObjectHeader + encoded payload).
  • Preserved packed-object chunk encoding/bytes on read so unchanged files can round-trip byte-identically.
  • Added tile-element serialization (TileElement.Write) and switched save logic to emit edited tile elements when available.
  • Corrected non-scenario game-state writing to emit the correct save struct variants (GameStateSave1/GameStateSave2).
  • Removed read-time state mutation that altered fix flags and broke binary stability.

• S5 structure correctness fixes

  • Fixed ScenarioOptions.LandDistributionPatterns to the correct array shape.
  • Corrected scenario Orders sizing to kMaxOrders.
  • Made S5Header serializable as a nested loco struct to support chunk-based object serialization paths.

• Editor behavior

  • Enabled SC5/SV5 save/save-as flow in the SCV5 view model.
  • Updated tile-element rendering/edit surface to expose subtype/sub-structure fields for in-editor modifications.

• Regression coverage

  • Added SC5 and SV5 round-trip tests that assert load -> save yields byte-identical output.

// Packed object write format now mirrors OpenLoco S5 layout.
foreach (var packedObject in PackedObjects)
{
    bytes.AddRange(packedObject.Header.Write().ToArray());
    bytes.AddRange(
        packedObject.RawChunk
        ?? SawyerStreamWriter.WriteChunkCore(packedObject.Data, packedObject.Encoding));
}

[Copilot]

🟡 Changes recommended

There are a couple of correctness issues in newly added save logic (file extension selection and packed-object header/count consistency) that can produce malformed or mis-typed output files.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR completes SC5/SV5 (S5) map-file round-trip support across the Dat serializer and the ObjectEditor UI, aiming for byte-identical load -> save output while also enabling in-editor modifications (notably tile elements and required objects).

Changes:

• Adds packed-object read/write support that preserves original encoded chunk bytes for byte-identical round-tripping.
• Implements tile-element serialization (TileElement.Write) and updates S5File.Write() to emit edited tile elements when present.
• Enables SCV5 Save/Save As in the editor and adds regression tests asserting byte-identical output for SC5/SV5.

File summaries

File	Description
Tests/SCV5SerializationTests.cs	Adds round-trip tests for SC5/SV5 asserting byte-identical load -> save.
Gui/Views/MainWindow.axaml	Switches the TileElement editor template to a PropertyGrid-based editor.
Gui/ViewModels/Loco/SCV5ViewModel.cs	Enables Save/Save As for SCV5 files and wires saving through S5File.Write().
Dat/Types/SCV5/TileElement.cs	Preserves the raw type byte and adds Write() for tile-element serialization.
Dat/Types/SCV5/ScenarioOptions.cs	Fixes LandDistributionPatterns to the correct array shape.
Dat/Types/SCV5/S5File.cs	Implements packed-object chunk round-tripping, correct save-variant writing, and tile-element emission.
Dat/Types/SCV5/GameStateSave1.cs	Fixes Orders array sizing to kMaxOrders.
Dat/Types/S5Header.cs	Makes S5Header an ILocoStruct to support nested struct serialization paths.

Review details

• Files reviewed: 8/8 changed files
• Comments generated: 4
• Review effort level: Lite

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