v0.9.0

Added — Phase C: async scorers, guest adapters, boxed Agent/Harness, Python workflow runner

Closes the "Phase B" deferral comments scattered across crates/agent,
crates/harness, crates/eval, and crates/py-bindings/src/{agent, harness,workflow,eval}.rs. The five blocks:

• AsyncScorer trait (crates/eval/src/scorer.rs). Parallel to
  the existing sync Scorer; blanket impl<S: Scorer> AsyncScorer for S keeps existing sync impls compatible. LlmJudgeScorer,
  RubricScorer, and PairwiseScorer now implement AsyncScorer
  directly — dropping the tokio::task::block_in_place workaround
  the sync Scorer impl required. EvalSuite::scorer field type
  changed from Arc<dyn Scorer> to Arc<dyn AsyncScorer>.
• 6 Python→Rust guest adapters (crates/py-bindings/src/guest/).
  The single-file guest.rs (331 LOC) is split into a guest/
  directory (10 files, ~1400 LOC). New adapters: PyInstructionAdapter,
  PyMemoryStrategyAdapter, PySkillStrategyAdapter, PyPersonaAdapter,
  PyMemoryStoreAdapter, PyEmbedderAdapter. Each ships a
  build_guest_* factory mirroring the existing build_guest_toolset
  pattern.
• BoxedAgent + AgentSpec::into_agent (crates/agent/src/boxed.rs).
  Object-erased BoxedAgent for config-driven instantiation. The typed
  Agent<I,T,Ms,Sk> keeps hot-path monomorphization; both share a
  pub(crate) async fn run_turn_impl helper.
• HarnessDispatch + HarnessRef + BoxedHarness (crates/harness/).
  Mirror of the Agent boxed-handle pattern. Harness::into_boxed,
  HarnessSpec::into_harness, and impl HarnessDispatch for Harness<L,T>
  added.
• PyAgent, PyHarness, PyWorkflowRunner Python wrappers with
  from_spec / from_dict constructors and async run_turn / run
  exposed as Python coroutines via
  pyo3_async_runtimes::tokio::future_into_py. WorkflowRunner::new
  was added as a public constructor.

Changed

• EvalSuite::scorer field type: Arc<dyn Scorer> →
  Arc<dyn AsyncScorer>. The blanket impl<S: Scorer> AsyncScorer for S means callers holding a sync Arc::new(SomeSyncScorer)
  continue to compile via auto-unsizing into the new field type.
  Direct &dyn Scorer callers of LlmJudgeScorer / RubricScorer
  must migrate to &dyn AsyncScorer — Rust coherence forbids both
  the blanket AsyncScorer impl and a direct Scorer impl on the
  same judge (ContainsScorer is unaffected).
• Sibling deps (atomr, atomr-infer, atomr-accel) consume
  crates.io artifacts only — no path = "../sibling/..." links.
  Pinned to atomr 0.9.2 / atomr-infer 0.8.0 / atomr-accel 0.10.0.