feat(runtime): add resident Wasmtime actor runtime

- define versioned service and clock WIT contracts
- enforce import allowlists, fuel, epoch, memory, I/O, and mailbox limits
- keep one Store and Component Instance resident per serial Actor
- add echo, counter, fault, spin, and capability probe components
- cover lifecycle, concurrency, sandbox, and fault recovery behavior

components/counter/src/lib.rs

@@ -0,0 +1,28 @@
+use core::sync::atomic::{AtomicU64, Ordering};
+
+mod bindings {
+    wit_bindgen::generate!({
+        path: "wit",
+        world: "counter-component",
+    });
+}
+
+static COUNTER: AtomicU64 = AtomicU64::new(0);
+
+struct Counter;
+
+impl bindings::Guest for Counter {
+    fn init(_config: Vec<u8>) -> Result<(), bindings::ServiceError> {
+        // Calls are serialized by the host Actor, so this component intentionally
+        // uses one mutable global to make resident memory observable in tests.
+        COUNTER.store(0, Ordering::Relaxed);
+        Ok(())
+    }
+
+    fn invoke(_input: Vec<u8>) -> Result<Vec<u8>, bindings::ServiceError> {
+        let next = COUNTER.fetch_add(1, Ordering::Relaxed).wrapping_add(1);
+        Ok(next.to_le_bytes().to_vec())
+    }
+}
+
+bindings::export!(Counter with_types_in bindings);