feat: reorganize examples and add signature support to JobBuilder

- Reorganized examples into osiris/, sal/, and utils/ folders
- Moved hardcoded scripts to separate .rhai files
- Added signature() method to JobBuilder for job signing
- Updated OSIRIS context to use block_in_place instead of runtime
- Removed runtime field from OsirisContext
- Added typed save() methods for Note and Event objects
- Updated all examples to use new structure and APIs

examples/sal/scripts/mycelium/mycelium_receive_message.rhai

@@ -0,0 +1,31 @@
+// Script to receive Mycelium messages
+
+// API URL for Mycelium
+let api_url = "http://localhost:2222";
+
+// Receive messages
+// This script will listen for messages on a specific topic.
+// Ensure the sender script is using the same topic.
+// -----------------------------------------------------------------------------//
+print("\nReceiving messages:");
+let receive_topic = "test_topic";
+let wait_deadline_secs = 100; 
+
+print(`Listening for messages on topic '${receive_topic}'...`);
+try {
+    let messages = mycelium_receive_messages(api_url, receive_topic, wait_deadline_secs);
+    
+    if messages.is_empty() {
+        // print("No new messages received in this poll.");
+    } else {
+        print("Received a message:");
+        print(`  Message id: ${messages.id}`);
+        print(`  Message from: ${messages.srcIp}`);
+        print(`  Topic: ${messages.topic}`);
+        print(`  Payload: ${messages.payload}`);
+    }
+} catch(err) {
+    print(`Error receiving messages: ${err}`);
+}
+
+print("Finished attempting to receive messages.");