feat(wfe-core): add typed workflow schema system

SchemaType enum with inline syntax parsing: "string", "string?",
"list<number>", "map<string>", nested generics. WorkflowSchema
validates inputs/outputs against type declarations at both compile
time and runtime. 39 tests for parse and validate paths.

wfe-core/src/models/mod.rs

@@ -7,6 +7,7 @@ pub mod lifecycle;
 pub mod poll_config;
 pub mod queue_type;
 pub mod scheduled_command;
+pub mod schema;
 pub mod status;
 pub mod workflow_definition;
 pub mod workflow_instance;
@@ -20,6 +21,7 @@ pub use lifecycle::{LifecycleEvent, LifecycleEventType};
 pub use poll_config::{HttpMethod, PollCondition, PollEndpointConfig};
 pub use queue_type::QueueType;
 pub use scheduled_command::{CommandName, ScheduledCommand};
+pub use schema::{SchemaType, WorkflowSchema};
 pub use status::{PointerStatus, WorkflowStatus};
 pub use workflow_definition::{StepOutcome, WorkflowDefinition, WorkflowStep};
 pub use workflow_instance::WorkflowInstance;