Fix dispatcher crash/deadlock, instruction analyzer, cache equality, task leak, and redirection protection

- MainThreadDispatcher: guard DispatchHook with try/catch so exceptions never escape to native caller; drain and fault pending work on Dispose; synchronize Execute/ExecuteAsync/Dispose against race/dispose.
- InstructionAnalyzer: require ModRM 0xEC for 0x83/0x81 sub-esp/rsp forms, rejecting unsafe RIP-relative or memory forms.
- PatternScannerCache: implement value equality on CacheKey so repeated scans actually hit cache.
- BackgroundTaskExecutor: add remote allocations to the free list immediately after VirtualAllocEx, before any write that could fail and leak.
- redirect: capture and restore original page protection in Apply/Remove instead of leaving target RWX.
- Regression tests for all six fixes.

Tests: 198 passing, 4 integration/interactive skipped.

WhiteMagic/Hooking/PrologueDecoder.cs

@@ -53,12 +53,12 @@ internal static class PrologueDecoder
                 return i + 2;
         }
 
-        // sub r/m32/64, imm8.
-        if (op == 0x83 && bytes.Length > i + 2)
+        // sub esp/rsp, imm8 — register-direct ModRM 0xEC only.
+        if (op == 0x83 && bytes.Length > i + 2 && bytes[i + 1] == 0xEC)
             return i + 3;
 
-        // sub r/m32/64, imm32.
-        if (op == 0x81 && bytes.Length > i + 5)
+        // sub esp/rsp, imm32 — register-direct ModRM 0xEC only.
+        if (op == 0x81 && bytes.Length > i + 5 && bytes[i + 1] == 0xEC)
             return i + 6;
 
         return -1;