Phase 6: Fix swallowed exceptions and cleanup unused usings

- Add debug logging to all empty catch blocks in DecalHarmonyClean.cs setup methods
  (prefix method catches intentionally stay silent to never break other plugins)
- Add error logging to VtankControl.VtSetSetting catch
- Add logging to DecalPatchMethods.ProcessInterceptedMessage catch
- Remove unused usings from PluginCore.cs (System.Diagnostics, System.Drawing,
  System.Text, System.Text.RegularExpressions)
- Flatten redundant nested try/catch in PatchPluginHost

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

MosswartMassacre/PluginCore.cs

@@ -1,13 +1,9 @@
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
-using System.Drawing;
 using System.Globalization;
 using System.Linq;
 using System.Net;
 using System.Runtime.InteropServices;
-using System.Text;
-using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using System.Timers;
 using Decal.Adapter;