v2.0.0rc182

Fix broken realtime logs and premature audit status on 202 calculations

After the threadpool refactor (4b819c5), two issues emerged for
background calculations triggered via HTTP 202:

1. Realtime WebSocket logs and `calculation_record` field stopped
   working because `copy_context()` only copies ContextVar bindings
   (references), not the underlying mutable objects. When the request
   thread exits `model_logging_context` and pops the instance from the
   shared ModelContext stack, the background thread's copied reference
   sees the same empty stack — ContextResolver.resolve() can no longer
   determine `current_record`, breaking WebSocket routing and DB
   persistence of CalculationLog entries.

   Fix: Set a fresh `ModelContext([instance])` at the start of
   `_invoke_calculate_hook` inside `ctx.run()`, giving the background
   thread its own independent model context.

2. AuditLogStatus was unconditionally marked 'success' in
   `perform_update` right after `serializer.save()`, even though the
   actual calculation hadn't started yet (only the field data was
   persisted). This gave operators a false impression that the
   operation completed successfully.

   Fix: Skip the immediate 'success' update when
   `instance._defer_calculate_hook` is set. The existing
   `ensure_terminal_calculation_audit` (called from
   `execute_calculation_sync` / `_finalize_pending_terminal_audit`)
   already handles setting the correct terminal status ('success' or
   'failure') once the calculation actually finishes.