nika-engine 0.38.0

Nika workflow engine — embeddable runtime, provider, DAG, and binding logic
nika-engine-0.38.0 has been yanked.

Nika Engine — Embeddable workflow execution engine

Module Architecture

┌──────────────────────────────────────────────────────────────┐
│                        DOMAIN MODEL                          │
│  ast/       YAML → Rust types (Workflow, Task, TaskAction)   │
└──────────────────────────────────────────────────────────────┘
                             │
                             ▼
┌──────────────────────────────────────────────────────────────┐
│                      APPLICATION LAYER                       │
│  runtime/   DAG execution (Runner, TaskExecutor)             │
│  dag/       DAG structure (Dag, validate)                    │
│  binding/   Data binding (WithSpec, ResolvedBindings)        │
└──────────────────────────────────────────────────────────────┘
                             │
                             ▼
┌──────────────────────────────────────────────────────────────┐
│                    INFRASTRUCTURE LAYER                      │
│  store/     State management (RunContext, TaskResult)         │
│  event/     Event sourcing (EventLog, EventKind)             │
│  provider/  LLM abstraction (rig-core wrapper)               │
└──────────────────────────────────────────────────────────────┘