Implement Tri-State Monad Error Handling

[AKRiLLiCK]

• Description: Implement the Monad tagged union (OK, NIL, ERR) marked with __attribute__((warn_unused_result)) and define the DOMAIN integer prefixes for error codes.
• Acceptance Criteria:
  • Define the Monad union combining void* val and u32 err_code.
  • Define core domain prefixes (e.g., DOMAIN_CAMELOT, DOMAIN_APP) and specific error codes (e.g., ERR_OUT_OF_MEMORY).
  • Tests must validate unpacking logic correctly routes to isolated union payloads without type punning corruption.