feat: async/parallel execution with configurable concurrency

Parallelize LLM calls across minibatches to reduce wall-clock time.
All domain ports (LLMPort, JudgePort, ProposerPort) are now async.
Adapter implementations wrap synchronous DSPy calls with asyncio.to_thread.
Judge calls run in parallel within a batch using asyncio.gather + semaphore.
Evaluator parallelizes minibatch execution with configurable concurrency.
Evolution loop and use case are fully async. Proposer stays sequential.
Added --max-concurrency CLI flag and max_concurrency YAML config field.
Added async_retry_with_backoff for async error handling.
All 139 unit tests pass.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

pyproject.toml

@@ -16,6 +16,7 @@ dependencies = [
 [project.optional-dependencies]
 dev = [
     "pytest>=8.3",
+    "pytest-asyncio>=0.24",
     "pytest-cov>=6.0",
     "ruff>=0.9",
     "mypy>=1.14",
@@ -37,6 +38,9 @@ target-version = "py312"
 python_version = "3.12"
 strict = true
 
+[tool.pytest.ini_options]
+asyncio_mode = "auto"
+
 [[tool.mypy.overrides]]
 module = ["dspy", "dspy.*"]
 ignore_missing_imports = true