feat: add instance_id actor primative

src/c/handle.cpp

@@ -66,4 +66,13 @@ auto thespian_handle_is_expired(thespian_handle h) -> bool {
           h)};
   return h_->expired();
 }
+
+auto thespian_handle_id(thespian_handle h) -> uintptr_t {
+  thespian::handle *h_{
+      reinterpret_cast<thespian::handle *>( // NOLINT(*-reinterpret-cast)
+          h)};
+  if (!h_)
+    return 0;
+  return thespian::instance_id(*h_);
+}
 }

src/thespian.zig

@@ -125,6 +125,12 @@ fn Pid(comptime own: Ownership) type {
             return c.thespian_handle_is_expired(self.h);
         }
 
+        /// Stable opaque actor identity. Two handles for the same actor
+        /// return the same value. Returns 0 for a null/expired handle.
+        pub fn instance_id(self: Self) usize {
+            return c.thespian_handle_id(self.h);
+        }
+
         pub fn wait_expired(self: Self, timeout_ns: isize) error{Timeout}!void {
             var max_sleep: isize = timeout_ns;
             while (!self.expired()) {