Add optional Iced backend: arbitrary text assembly and full prologue validation

Section 8 of the whitemagic-foundation change.

- 8.1: reference Iced 1.21.0 behind IcedAssembler:IAssembler. The default
  StubAssembler path never touches Iced; only constructing IcedAssembler pulls
  it into a behavioral path.
- 8.2: IcedAssembler.Assemble bridges Intel-syntax text onto Iced's fluent
  Assembler by reflection (Iced ships no text parser). Registers, immediates and
  labels are supported with origin-relative encoding; memory operands throw
  NotSupportedException.
- 8.3: IcedAssembler.GetPrologueLength decodes arbitrary instructions via Iced's
  Decoder. DetourManager.PrologueLengthResolver (new delegate) defaults to the
  built-in PrologueDecoder and is swappable to the Iced resolver, threaded into
  each Detour. This lifts the "partial boundary safety" caveat on the hooking
  slice when Iced is opted in.

Also gitignore test-run TestResults artifacts.

Tests: 221 passing, 4 skipped.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -10,3 +10,7 @@ reference/
 # Scratch
 *.tmp
 *.log
+
+# Test run artifacts
+WhiteMagicTest/TestResults/
+**/TestResults/