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

crates/wasmeld-runtime/src/bindings.rs

@@ -0,0 +1,16 @@
+//! Typed host and guest bindings generated from independently versioned WIT packages.
+
+// The service world defines the exports every runnable component implements.
+wasmtime::component::bindgen!({
+    path: "../../wit/service",
+    world: "service-component",
+});
+
+pub(crate) mod clock {
+    // Host capabilities are generated separately so adding a capability does
+    // not expand the baseline service contract for every component.
+    wasmtime::component::bindgen!({
+        path: "../../wit/clock",
+        world: "clock-host",
+    });
+}