[logging] Migrate SelfLoader and DirectExecutionBackend.Diagnostics to SharpEmuLog (#65)

Phase 2 of Console.Error.WriteLine → structured logging migration.

SelfLoader.cs (30 sites):
- Category: "Loader"
- TLS load_start/load_done, Segment info, DTPMOD64 patching → Debug
- ELF alignment mismatch, invalid symbol value skips, CRITICAL invalid patch → Warning
- Runtime symbol index populated, Initializers discovered → Info
- [FOCUS][SCAN/SKIP] relocation trace, [RELOC] target trace → Debug
- TryLoadTableBytes diagnostics → Debug (FAILED → Warning)
- ResolveMappedAddressOrFallback trace → Debug

DirectExecutionBackend.Diagnostics.cs (17 sites):
- Category: "Native" (Log field in main DirectExecutionBackend.cs partial)
- DumpRecentImportTrace → Info
- Suspicious unresolved pointer hits/cap → Warning
- ProbeReturnRip return-rip bytes/slots/PLT trace → Debug

Level mapping: [TRACE]/[FOCUS]/[RELOC]/[TEST] → Debug; [INFO] → Info;
[WARNING]/WARNING/CRITICAL/Skipping/FAILED → Warning.

[LOADER] prefix dropped — category is in LogEntry.

Console.WriteLine (stdout, ~25 sites in SelfLoader.cs) intentionally
left untouched — only Console.Error.WriteLine was in scope.

Build: 0 errors, 0 warnings.

Co-authored-by: Hermes Atlas <hermesatlas@example.com>

src/SharpEmu.Core/Cpu/Native/DirectExecutionBackend.cs

@@ -11,11 +11,13 @@ using SharpEmu.Core.Cpu;
 using SharpEmu.Core.Loader;
 using SharpEmu.Core.Memory;
 using SharpEmu.HLE;
+using SharpEmu.Logging;
 
 namespace SharpEmu.Core.Cpu.Native;
 
 public sealed unsafe partial class DirectExecutionBackend : INativeCpuBackend, IGuestThreadScheduler, IDisposable
 {
+	private static readonly SharpEmuLogger Log = SharpEmuLog.For("Native");
 	private const int ImportLoopHistoryLength = 2048;
 
 	private const int ImportLoopWideDiversityWindow = 768;