[Comgr][hotswap] Add raise_failure + RaiseContext + register file

[tgymnich]

Foundation infrastructure consumed by every per-format handler:

• raise_failure.{h,cpp} — RaiseFailure value type with structured
  Reason, Mnemonic, Format, Detail, etc. fields plus typed
  factories (unsupportedOpcode, unsupportedShape, bailReason,
  ...). Carries the diagnostic data the kerneldex coverage runner
  bucketizes on.
• raise_context.{h,cpp} — RaiseContext is the per-kernel mutable
  state every handler reads and writes: LLVMContext / Module / IR
  builder, decoded inst stream, register file, kernarg layout,
  user-SGPR layout, ISA profile, wave projection, lane-active mask
  cache, the pending failure for read-path errors, etc.
• reg_file.{h,cpp} — AllocaRegFile models the AMDGPU SGPR/VGPR/AGPR
  register files as an alloca-per-physical-reg promoted to SSA by
  Phase 6 mem2reg. readReg{32,64,Vec} / writeReg{32,64,Vec}
  handle the bitcasts handlers don't want to repeat.
• kernarg_layout.{h,cpp} — KernargLayout builds the byref placeholder
  type the lifted IR's first parameter takes. Mirrors the source
  kernel's MsgPack-derived offset/size layout.
• user_sgpr_layout.{h,cpp} — UserSgprLayout::tryFromKernelMeta
  derives the source SGPR ABI (workgroup id / private segment buffer
  / kernarg ptr / kernarg-preload SGPRs) from the kernel descriptor.
• handlers.h — forward declarations for every handleXXX entry
  point. Concrete handler files come in subsequent commits.

[tgymnich]

Warning

Stacked PR

1. [Comgr][hotswap] Add bare-bones hotswap transpiler scaffolding #2438
2. [Comgr][hotswap] Add code-object metadata parsing #2437
3. [Comgr][hotswap] Add AMDGPU MC state setup #2439
4. [Comgr][hotswap] Add DecodedInst + basic kernel decoder #2517
5. [Comgr][hotswap] Add wave projection + ISA profile + abi/wave-mask docs #2518
6. [Comgr][hotswap] Add raise_failure + RaiseContext + register file #2551 <----
7. [Comgr][hotswap] Add raise_cli + lit harness for hotswap-raise fixtures #2552
8. [Comgr][hotswap] Add SOPP + SOPC handlers #2553