Make eager activity reservation limit configurable

[Sushisource]

What changed

• Add max_eager_activity_reservations_per_workflow_task to Worker and its configuration types.
• Forward the configured value through the Python bridge into Core.
• Preserve the existing default of three.
• Reject non-positive values with guidance to use disable_eager_activity_execution=True to disable eager execution.
• Update the Core submodule to the merged configurable-limit implementation.

Why

Core already caps the number of slots it attempts to reserve for eager activities while completing a workflow task. This exposes that existing cap to Python users without introducing a separate execution-lifetime limit.

Validation

• poe format
• poe build-develop
• poe bridge-lint
• Focused Pyright check for the changed worker and replay paths
• uv run pytest tests/worker/test_worker.py::test_worker_max_eager_activity_reservations_per_workflow_task_config tests/worker/test_worker.py::test_worker_rejects_non_positive_max_eager_activity_reservations -q

The broad lint/test collection additionally requires optional contrib dependencies that are not installed in this workspace. No breaking changes; the default remains three.