v0.2.1 list filter parity

Every list_* MCP read tool now passes through the full hatchet-sdk (or REST) filter signature. Closes the parity gaps surfaced by an audit; one underlying refactor (a shared _parse_enum single-value validator).

Added

• list_runs now forwards two SDK filters that were previously hidden from MCP clients: parent_task_external_id (expand a sub-workflow tree from a parent run) and triggering_event_external_id (trace which runs an event caused) (src/hatchet_mcp/tools/runs.py).
• list_scheduled now forwards three SDK filters: parent_workflow_run_id, order_by_field (triggerAt / createdAt), and order_by_direction (ASC / DESC) (src/hatchet_mcp/tools/schedules.py). Invalid order_by_* values raise with the allowed-values list rather than reaching the SDK.
• list_crons now forwards order_by_field (name / createdAt) and order_by_direction (ASC / DESC) (src/hatchet_mcp/tools/schedules.py).
• list_events now forwards event_ids (specific events by UUID) and scopes (filter by event scope strings) (src/hatchet_mcp/tools/events.py).
• list_rate_limits now forwards order_by_field (key / value / limitValue) and order_by_direction (lowercase asc / desc, matching the SDK's RateLimitOrderByDirection enum — distinct from WorkflowRunOrderByDirection's uppercase) (src/hatchet_mcp/tools/observability.py).
• New shared helper _parse_enum for validating a single (str) enum value, mirroring _parse_enum_list (src/hatchet_mcp/_shared.py).